MANIFOLDSmedia.wattswater.com/RadiantPEXManual.pdf · mum of 2" of portland concrete mix above the RadiantPEX; more may be required depending on structural loading. Use a foil-faced

© 2003 Watts Radiant RadiantPEX Installation Manual LIT#PEXMAN0803 Effective 08/01/2003

Cross-Linked Polyethylene Tubing with EVOH Barrier

®

C O D E S , L I S T I N G S , A N D S TA N D A R D SRadiantPEX is manufactured in accordance with American Standard

Testing Methods F-876 and F-877, is Certified by NSF to Standards 14 and 61, and is listed by the International Conference of BuildingOfficials (ICBO) Report #ER-6080 and the International Association ofPlumbing and Mechanical Officials (IAPMO) carrying the UniformPlumbing Code symbol. All RadiantPEX pipe sold in Canada is approvedto CSA Standard B137.5.

CustomCut manifolds.

RadiantPEX

Stainless steel manifolds.

Swedged copper manifolds.Standard all-brass manifolds.

Cast brass manifolds.

CrimpAll™ Tool

Tools for 3/8", 1/2", 5/8", 3/4", 1" connections.

M A N I F O L D SWatts Radiant offers a wide range of manifolds for RadiantPEX.

Manifolds can be outfitted with CrimpRing or T-20 Compression fittings, with or without mini-ball valves. Additional accessories include unions, isolation valves, temperature gauges, vent/purge assemblies, actuators, and visual flow indicators. Other options can be found on the Watts Radiant RadiantPEX Submittal or in the Watts Radiant product catalog on our Web site.

Triple-track Railway™ LockDown™Fastener

Foamboard ScrewClip

FoamboardStaples

ClipTie™Fastener

SnapClip™ and StrapDown™ installed in ClipRail™

TM

BEND STANDARD FLUID CAPACITYNOMINAL I .D. O.D. RADIUS COIL LENGTHS PER 100'

3/8" RadiantPEX 3/8" 1/2" 4" 600' 0.50 Gal.

1/2" RadiantPEX 1/2" 5/8" 5" 100'/300'/600'/1000' 0.92 Gal.

5/8" RadiantPEX 5/8" 3/4" 6" 600'/1200' 1.4 Gal.

3/4" RadiantPEX 3/4" 7/8" 7" 100'/600'/1200' 1.8 Gal.

1" RadiantPEX 1" 1-1/8" 10" 600' 3.0 Gal.

RadiantPEX is a cross-linked polyethylene tubing manufactured with an EVOH oxygen barrier. Allsizes meet ASTM F-876 standards and are manufactured to SDR 9 dimensions. It is shipped in 100'to 1200' length boxed coils in 3/8", 1/2", 5/8", 3/4", and 1" sizes.

In the United States:

Watts Radiant3131 W. Chestnut Expwy.Springfield, MO 658021-800-276-2419 toll-free417-864-6108 phone417-864-8161 faxwww.wattsradiant.com

In Canada:

Watts Industries–Canada5435 North Service RoadBurlington, ON L7L 5H71-888-208-8927 toll-free phone905-332-4090 phone1-888-882-1979 toll-free fax905-332-7068 faxwww.wattscanada.ca

C R I M P R I N G T O O L : F A S T E N I N G S Y S T E M S :

This RadiantPEX Installation Manual repre-

sents the collective knowledge of thousands of

our customers who have been kind enough to

help us with ideas and techniques that have

worked for them. We have selected the best of

these ideas and rigorously refined them.

This refining process is based on the collective

wisdom that comes from having an engineering

and technical staff with well over 100 years of

combined experience with modern floor heating

and snowmelting. Please take the time to

carefully read this manual before installing your

floor heating or snowmelting system.

PLEASE NOTE:

This manual only covers installation of Watts Radiant’s

RadiantPEX tubing, and should not be used for the installa-

tion of our Onix radiant hose.

This is not a design manual. For design assistance, we

encourage you to contact us or our representatives for a

design analysis using Watts Radiant’s RadiantWorks®

system design software.

Before designing or installing a radiant heating or snow-

melting sytstem, you should always consult with local,

experienced design and installation professionals to ensure

compliance with local building practices, climate conditions,

state and local building codes, and past customs.

Snowmelting Applications

Slab over Existing Slab Used when placing a new radiant slabdirectly over an existing slab. A great application whenthe slab will be sub-jected to heavy loads.

Where space permits, we recommend the use ofextruded polystyrene (Dow®

Blue Board®) insulation at theperimeter of the new slab. The use ofpoly-fiber material in the new concrete slab will add crack resistance.

In this application the RadiantPEX can be tied to rewire or poultrynetting depending on the structural needs of the project.

Typical Slab SnowmeltThis is the most popular application in snowmelting and it provides the best snowmelting performance.

Install RadiantPEX mid-way in the slab or at adepth that will provide aminimum of 3" of concreteover the top of the RadiantPEX;more may be required depending onstructural loading.

The size and spacing of RadiantPEX varies widely in snowmelting projects and is based on many variables. Always refer to specificdesign information for the project.

Also, drainage is important in snowmelting. Make sure provisionsare made to safely carry away the melt water.

Note that insulation is not required in this application.

Slab over Steel DeckFasten the RadiantPEX in place and then cover it with a mini-mum of 2" of portlandconcrete mix abovethe RadiantPEX; more may be required depending on structuralloading.

Use a foil-faced insulation forthis application, with the foil facingup, and a 2" minimum air space between thefoil surface and the steel deck.

Sprayed-on insulation also works well in this application.

Brick Paver SnowmeltThis is a popular choice when brick pavers are being installedin an entrance, courtyard,driveway or other outdoor area where snow and ice removal is needed.

RadiantPEX is installed in asand or crushed stone base, thensecured with wire hooks every 2' along itslength. A layer of sand is then placed over theRadiantPEX and compacted to provide a minimum of 1" coverage above the top of the RadiantPEX (more may be requireddepending on structural loading). The brick pavers are theninstalled on the compacted base material.

The size and spacing of RadiantPEX varies widely in snowmeltingprojects and is based on many variables. Always refer to specificdesign information for the project. Also, drainage is important insnowmelting. Make sure provisions are made to safely carry awaythe melted water.

Note that insulation is not required in this application.

Warm up a concrete slab to provide space heat.

Install a minimum of 2" of concrete above the top of theRadiantPEX for residential and 3" for commercial floor heat applications. You may need a greater thickness over theRadiantPEX, depending on structural loading.

Use an extruded polystyrene (Dow® Blue Board®) insulation board on the edge of, and optionally under the slab, depending on site conditions.

Slab on Grade

page 2 Watts Radiant: RadiantPEX Installation Manual

Table of ContentsSection Page

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6Heat Transfer Basics . . . . . . . . . . . . . . . . . . . . . . . . . . .6RadiantPEX Tubing . . . . . . . . . . . . . . . . . . . . . . . . . . .6General RadiantPEX Installation Precautions . . . . . .8The Design Process . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Step 1: Initial Design Considerations . . . . . . . . . . . . .12Floor Coverings . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Tile Floors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13Hardwood Flooring . . . . . . . . . . . . . . . . . . . . . . .13

Controlling Moisture . . . . . . . . . . . . . . . . . . . . .14Installation Cautions . . . . . . . . . . . . . . . . . . . . .15

Carpet and Pad Flooring . . . . . . . . . . . . . . . . . . .16Step 2: Radiant Zoning . . . . . . . . . . . . . . . . . . . . . . . .16

1. Zoned by Floor Coverings . . . . . . . . . . . . . . . . .162. Zoned by Occupancy . . . . . . . . . . . . . . . . . . . . .163. Zoned by Construction . . . . . . . . . . . . . . . . . . .164. Zoned by Mechanical Considerations . . . . . . . .17

Step 3: Manifold Location . . . . . . . . . . . . . . . . . . . . .17Step 4: Heat Loss Calculations . . . . . . . . . . . . . . . . . .18

Using RadiantWorks® Reports . . . . . . . . . . . . . . . .19Zone List Report . . . . . . . . . . . . . . . . . . . . . . . . .19Assumption Report . . . . . . . . . . . . . . . . . . . . . . .20Heat Loss Report . . . . . . . . . . . . . . . . . . . . . . . . .20

Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20Frame Floors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20Design Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . .21

RadiantPEX Spacing . . . . . . . . . . . . . . . . . . . . . . . .21Perimeter Banding . . . . . . . . . . . . . . . . . . . . . . . . . .21

UnderFloor Applications . . . . . . . . . . . . . . . . . . . . . . . .22Installation Methods . . . . . . . . . . . . . . . . . . . . . . . .22Heat Transfer Plates . . . . . . . . . . . . . . . . . . . . . . . . .22Suspended . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23Installation Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Step 1: Install Manifolds . . . . . . . . . . . . . . . . . . . . .24Step 2: Zone Boundaries . . . . . . . . . . . . . . . . . . . . .24Step 3: Tubing Requirements . . . . . . . . . . . . . . . .24Step 4: Drill Joists . . . . . . . . . . . . . . . . . . . . . . . . . .24Step 5: Install the Fasteners . . . . . . . . . . . . . . . . . .25Step 6: Install the RadiantPEX . . . . . . . . . . . . . . .27Step 7: Repeat with Next Circuit . . . . . . . . . . . . . .29Step 8: Visual Inspection and Pressure Test . . . . . .30

Insulation Details . . . . . . . . . . . . . . . . . . . . . . . . . . . .30TJI Joists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30Open Web Trusses . . . . . . . . . . . . . . . . . . . . . . . . . .31

UnderFloor Applications

ZONE 1

ZONE 2AZONE 2

Typical radiant zoning.

Watts Radiant: RadiantPEX Installation Manual page 3

Section Page

Sandwich/SubRay® Applications . . . . . . . . . . . . . . . . .32Installation Methods . . . . . . . . . . . . . . . . . . . . . . . . . .32

Heat Transfer Plates . . . . . . . . . . . . . . . . . . . . . . . . .32Clips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33SubRay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33Tools and Materials Required . . . . . . . . . . . . . . . . .33

Fasteners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Installation Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

Step 1: Install Manifolds . . . . . . . . . . . . . . . . . . . . .34Step 2: Zone Boundaries . . . . . . . . . . . . . . . . . . . . .34Step 3: Tubing Requirements . . . . . . . . . . . . . . . . .34Step 4: Sleeper Placement and Sizing . . . . . . . . . .35Step 5: Install the Fasteners . . . . . . . . . . . . . . . . . .35Step 6: Install the RadiantPEX . . . . . . . . . . . . . . . .36Step 7: Repeat With Next Circuit . . . . . . . . . . . . . .37Step 8: Visual Inspection and Pressure Test . . . . . .37

Insulation Details . . . . . . . . . . . . . . . . . . . . . . . . . . . .37Walls and Ceilings . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Recessed Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39SubRay 862 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39Cautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Slab-on-Grade Applications . . . . . . . . . . . . . . . . . . . . .41Site Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41Insulation Details . . . . . . . . . . . . . . . . . . . . . . . . . . . .42

Type of Insulation . . . . . . . . . . . . . . . . . . . . . . . . . .42Special Construction Considerations . . . . . . . . . . . . .42

Control Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42Design Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . .42

RadiantPEX Spacing . . . . . . . . . . . . . . . . . . . . . . . .42Perimeter Banding . . . . . . . . . . . . . . . . . . . . . . . . . .43Tools Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

Slab Profile and General Details . . . . . . . . . . . . . . . . .44Installation Steps . . . . . . . . . . . . . . . . . . . . . . . . . . .44

Step 1: Pre-Pour Conditions . . . . . . . . . . . . . . . . .45Step 2: Install Manifolds . . . . . . . . . . . . . . . . . . .45Step 3: Determine Zone Boundaries . . . . . . . . . .46Step 4: Tubing Requirements . . . . . . . . . . . . . . . .46Step 5: Install the RadiantPEX . . . . . . . . . . . . . .46Step 6: Secure the RadiantPEX . . . . . . . . . . . . . .46Step 7: Repeat With Next Circuit . . . . . . . . . . . .47Step 8: Visual Inspection and Pressure Testing . .47Step 9: The Concrete Pour . . . . . . . . . . . . . . . . . .47

Sandwich/SubRay Applications

Slab-on-Grade Applications

Table of Contents


Section Page

Thin-Slab and Slab-Cap Applications . . . . . . . . . . . . .48Design Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

RadiantPEX Spacing . . . . . . . . . . . . . . . . . . . . . . . .48Perimeter Banding . . . . . . . . . . . . . . . . . . . . . . . . . .49Tools and Materials Required . . . . . . . . . . . . . . . . .49Fasteners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Watts Radiant Staple Gun . . . . . . . . . . . . . . . . . . . .50

Installation Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50Step 1: Install Manifolds . . . . . . . . . . . . . . . . . . .50Step 2: Determine Zone Boundaries . . . . . . . . . .50Step 3: Tubing Requirements . . . . . . . . . . . . . . . .50Step 4: Install the RadiantPEX . . . . . . . . . . . . . .50

Walls and Built-ins . . . . . . . . . . . . . . . . . . . . . . .51Step 5: Secure the RadiantPEX . . . . . . . . . . . . . .51Step 6: Repeat With Next Circuit . . . . . . . . . . . .51Step 7: Visual Inspection and Pressure Test . . . .52

Insulation Details . . . . . . . . . . . . . . . . . . . . . . . . . . . .52Thin Slab with Sleepers . . . . . . . . . . . . . . . . . . . . . .52Steel Deck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53Precast Slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53

Snowmelt Applications . . . . . . . . . . . . . . . . . . . . . . . . .54Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54Brick Paver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54General Site Preparation . . . . . . . . . . . . . . . . . . . . . . .55Insulation Details . . . . . . . . . . . . . . . . . . . . . . . . . . . .55Control Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56Design Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . .56

RadiantPEX Spacing . . . . . . . . . . . . . . . . . . . . . . . .56Tools and Materials Required . . . . . . . . . . . . . . . . .56

Application Profiles and General Details . . . . . . . . . .58Installation Steps . . . . . . . . . . . . . . . . . . . . . . . . . . .58

Step 1: Pre-Pour Conditions . . . . . . . . . . . . . . . . .58Step 2: Install Manifolds . . . . . . . . . . . . . . . . . . .58Step 3: Determine Zone Boundaries . . . . . . . . . .59Step 4: Tubing Requirements . . . . . . . . . . . . . . .59Step 5: Install the RadiantPEX . . . . . . . . . . . . . .59Step 6: Secure the RadiantPEX . . . . . . . . . . . . . .60Step 7: Repeat With Next Circuit . . . . . . . . . . . .60Step 8: Visual Inspection and Pressure Test . . . .60Step 9: The Concrete Pour . . . . . . . . . . . . . . . . . .60

Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61Glycol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

Thin-slab and Slab CapApplications

Snowmelt Applications

Table of Contents


Section Page

Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63Manifolds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63

Factory-Supplied Manifolds . . . . . . . . . . . . . . . . . .63Field-Constructed Manifolds . . . . . . . . . . . . . . . . . .63Manifold Set-Up . . . . . . . . . . . . . . . . . . . . . . . . . . .65

RadiantPEX Circuit Balancing Valves . . . . . . . . . . . . .66RadiantPEX Fittings . . . . . . . . . . . . . . . . . . . . . . . . . . .66Field Repairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67Pressure Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68Nomograph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69Pressure Drop Charts . . . . . . . . . . . . . . . . . . . . . . . . . .70 RadiantPEX No-Sweat Baseboard, Fan Coil,and Manifold Connection . . . . . . . . . . . . . . . . . . . . . .74

Connection Details . . . . . . . . . . . . . . . . . . . . . . . . . .74Near Boiler Piping and Controls . . . . . . . . . . . . . . . . .75Primary/Secondary . . . . . . . . . . . . . . . . . . . . . . . . . . .75Point of No Pressure Change . . . . . . . . . . . . . . . . . . .75Circulator Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75

Step 1: Determine Zone Flow Rate . . . . . . . . . . . .76Step 2: Determine Circuit Flow Rate . . . . . . . . . . .76Step 3: Determine Zone Pressure Drop . . . . . . . . .76Step 4: Determine Supply/Return

Pressure Drop . . . . . . . . . . . . . . . . . . . . . . . . . . . .76Step 5: Determine Complete Pump Spec . . . . . . . .76

Expansion Tank Sizing . . . . . . . . . . . . . . . . . . . . . . . .76Mixing Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78

Mix Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78Injection Pump Sizing . . . . . . . . . . . . . . . . . . . . . . .79

General Schematics . . . . . . . . . . . . . . . . . . . . . . . . . . .81

Manifold Options

Piping

Table of Contents


Welcome to the exciting world of radiant floor heating and snowmelting.For some, this manual will be an intro-duction to installing floor heating andsnowmelting projects. For others,these jobs are second nature. Thismanual is designed to help both thenovice and expert, with informationranging from basic heat transfer tomore complex system design and trouble-shooting.

With the ever-increasing sophisticationof the radiant industry, Watts Radiantoffers an expanded product offeringthrough its worldwide network ofcompanies. The best of what theUnited States and Europe have to offercan be found at Watts Radiant.

Watts Radiant also offers a wide range of support options, from localwholesalers and representatives to our toll-free number direct to the factory, for help answering those difficult questions.

When you select Watts Radiant, youselect an entire support team.

Heat Transfer Basics

One of the goals of this manual is toenable installers to make better deci-sions on the job site. These decisionscan range from modifying a layout toaccount for a room change to deter-mining what effect added windowshave on a room’s heat loss.

To better address these types of con-cerns, you must understand how aradiant system works. All forms ofheating work on three basic modes ofheat transfer: Convection, Conductionand Radiant.

Convective Heat Transfer is the mostfamiliar type of heat. All forced-airsystems are convective heat transfersystems. This includes hydronic base-boards and fan coils.

Conductive Heat Transfer is energymoving through an object. Place a

Introduction

metal pot on the stove and in a fewminutes the handle is hot.

Radiant Heat Transfer is the leastunderstood, but is the one that is mostimportant in our daily lives. Radiantheat transfer is the exchange of energyfrom a hot source to a cold source.The sun is typically used to illustratethis mode of transfer.

Regardless of the type of heating system used, all follow one basic rule.Hot always moves to cold. Place yourhand under a lamp and your handbegins to get warm. This is becausethe lamp is hotter than your hand andis trying to lose energy to its coolersurroundings.

In most cases all three forms of energytransfer are present in radiant floorheating systems.

In a RadiantPEX UnderFloor™ applica-tion, Convection is present in the joistcavity, Conduction moves the energyfrom the cavity and tubing through thefloor, and Radiant energy is broadcastfrom the floor to the cold objects inthe room.

If these basic principles are under-stood, then any project will be a suc-cess. Just remember to think like heat;moving from hot to cold.

RadiantPEX Tubing

This manual is to be used with Watts Radiant’s RadiantPEX tubing, a cross-linked polyethylene, or PEXfor short. It should not be used toinstall Onix tubing.

Watts Radiant has long been a recog-nized leader in the manufacture andengineering of radiant floor heatingand snow melt systems.

The cross-linked molecular structureof RadiantPEX offers toughness, flexibility and lasting durability.RadiantPEX is corrosion resistant andvirtually maintenance free. This PEXtubing withstands temperatures ranging from below freezing to 180°F.RadiantPEX combines all of the traditional advantages of plastic PEXtubing, but with an EVOH oxygen barrier. This barrier provides addedprotection against corrosion for thevarious ferrous components of a heating system.

RadiantPEX is manufactured to meetthe American Standard Testing Methodfor cross-linked Polyethylene Tubing(ASTM F-876) and all sizes are madeto the Standard Dimension Ratio forPEX pipes, SDR-9.


Although RadiantPEX is used most inradiant floors, it can be used for otherapplications, such as supply and returnlines for baseboard and fan coils.

Even though RadiantPEX is an excep-tional choice for radiant applications,there are some installation featuresthat need to be addressed.

PEX tubing will expand and contractwith temperature changes (unless it isembedded in a cementious material).The amount of movement is directlyproportional to the temperatureincrease. All PEX tubing options willexpand 1.1" for every 10°F rise intemperature for every 100' of pipe. Forexample, a system uses 300' runs of1/2" RadiantPEX and is filled using60°F water. The system is heated to160°F, which is a change of 100°F, orten 10° increments. Each circuit in thissystem will expand:

1.1"/10' × 10' × 3 = 33"

In this example, the PEX circuits willmove approximately 33" as the systemheats up and cools down.

In most cases this can lead to a potential noise issue, especially if theRadiantPEX is installed in a framefloor application.

If noise is a concern, certain precau-tions can be taken to minimize oreliminate noise, such as constant circulation, injection mixing, heattransfer plate or suspension attach-ments methods. Each of these optionswill be addressed in detail in this manual. Remember, PEX in slabs andthin slabs is not subject to movement.

Although various attachment methodsand application conditions may allowfor tighter than 6"–8" on center (OC)

spacing of the RadiantPEX, it isadvised not to go tighter. Closer spac-ings increase the risk of kinking thebends. Standard bend radius for anysize PEX piping should not exceed 8 times the nominal outside diameter.

RadiantPEX Sizes

Watts Radiant offers a wide range ofRadiantPEX sizes, from 3/8" to 1"nominal internal diameter (ID). It is amisconceived notion that a largerdiameter tubing will offer greater heatoutput. A 3/8" circuit of RadiantPEXwill generate the same amount of heatoutput as 1/2". The main difference isthe flow capability. Larger diametertubing allow for the same flow rates atlower head pressures, or friction loss.For most residential and light commer-cial heating, 200' lengths of 3/8" or300' lengths of 1/2" RadiantPEX areused. For snowmelting and largercommercial applications, 1/2" to 1"RadiantPEX will be used.

Using WaterPEX for RadiantApplications

Throughout this manual, we refer to all Watts Radiant PEX as“RadiantPEX”. However, there areapplications where non-barrierWaterPEX can be used. If WaterPEXis selected for any heating orsnowmelting application, we highlyrecommend protecting the ferrous system components from possible corrosion. This can be done by usingnon-ferrous components, separatingferrous components with the use of aheat exchanger, or installing a suitablewater or glycol system treatment.

Introduction

ID Bend Fluid Volume Typical Max Max FactorySize Radius per 100' Installed Length Length*

3/8" 4" 0.53 gal. 200' 600'1/2" 5" 0.96 gal. 300' 1000'5/8" 6" 1.40 gal. 400' 1,200'3/4" 7" 1.90 gal. 500' 1,200'1" 10" 3.10 gal. 600' 600'

*Lengths indicated are maximum available coil lengths. Smaller coil sizes are available.Call Watts Radiant for minimum quantities for special orders.

R5"R5"R5"

4" 6" 8"

Typical bend radii for 1/2" diameter RadiantPEX. Larger diameter tubing will require larger bend radii.

Illustration showing the layered construction of RadiantPEX tubing.

EVOH Oxygen Barrier

Adhesive LayerCross-linkedPolyethylene

stress, strain, and thermal expansionand contraction.

Most codes require the use ofapproved fastening devices. It is veryimportant that plastic fasteners areused for mounting to wood membersstuds, joists, or plywood. Use a specialstand-off type fastener like theStrapDown™ or SnapClip™ to make

Installation Precautions


General RadiantPEXInstallation Precautions

Do Not Use Incompatible(Non–SDR-9) Pipe and Fittings

There are a few incompatible types ofpipe and fittings that look similar toSDR-9 materials, but are made toslightly different dimensions. All com-patible PEX pipe will be labeled asmeeting the ASTM 876/877 Standard.

Polybutylene Pipe and Fittings.The same crimp tools used for SDR-9RadiantPEX were also used on theolder polybutylene pipe, but the fittings and CrimpRings are not com-patible. Note that the SDR-9RadiantPEX CrimpRings are coloredblack so that you can avoid cross-contaminating your parts bins witholder polybutylene fittings.

European PEX Pipe and Fittings.Most PEX pipe made in Europe,unless specifically stated otherwise, isnot made to the SDR-9 standard. Itmay look the same, but do not usethese materials with SDR-9 pipe andfittings. Some older PEX pipe made inNorth America was also made to thisEuropean dimensional standard. Becareful not to mix the two types.

Protect from Physical Damage

Although RadiantPEX pipe is, inmany respects, a durable material, itmust be stored, installed, and protectedproperly to ensure a quality job.Following are some key points toalways keep in mind.

Do Not Exceed the Minimum Bend Radius.The minimum bend radius forRadiantPEX pipe is 8 times the out-side diameter of the pipe. Dependingon the temperature of the pipe,whether it is being rolled with oragainst the curvature of the roll, andthe speed at which the bend is made,this number may be somewhat more.

Use RadiantPEX bend supports tohold a bend at the correct radius and to hold the pipe in place. If you kinkthe pipe you may be able to reform it.See page 11 for how to reformRadiantPEX tubing if it is kinked.

Support the PEX Properly.Although RadiantPEX is strong, itmust be supported against undue

StrapDown PEX fastener (top) and the SnapClip fastener (bottom). These fasteners are used for makingvertical or horizontal supply/return runs to manifolds or other distribution points.

PEXScrew

Screw

PEX

Minimum bend radius (left) for RadiantPEX, or 8 times the diameter of the pipe. (Right) RadiantPEX bentto radius less than minimum. Tubing is strained, becomes oval, and may kink or fail.

Installation Precautions


vertical or horizontal supply/returnruns to manifolds or other distributionpoints. Use these for mounting to steelframing members, as well. Use theLockDown™ fastener for UnderFloorSandwich floor-heating applications.

Vertical Runs. Vertical runs must besupported at least at every floor level.We recommend every 30".

Horizontal Runs. Where the pipe isfastened to the side of floor joists itshould be supported every 30". If it is continuously supported the pipe can bestrapped down every 6'.

Terminate RadiantPEX with Care.Always leave enough excess tubing at the beginning and end of runs tomake connections without puttingstrain on the tubing and/or connection.Do not bend RadiantPEX tubing on a radius smaller than 8 times the diameter of the pipe. If bendingagainst the coil, the allowed bendingradius is 24 times the diameter of thepipe. Damaged pipe must be cut outand replaced.

Trenching Precautions.Where RadiantPEX is laid in a trench,snake the pipe in with sufficient“waves” in the pipe so that there is

Support horizontal and vertical runs every 30" with Watts Radiant’s StrapDown or SnapClip fasteners.

Use the LockDown fastener to support the PEX in UnderFloor Sandwich applications.

PEX

Screw

sufficient allowance for expansion andcontraction with temperature changesin the pipe.

RadiantPEX can be damaged by abrasion and by contact with abrasivematerials, such as fill material withsharp edges. It is essential that the soil in the trench provide stable, continuous support for the pipe. Play it safe by installing polyethylene pipe insulation around the tubing forprotection.

Always ensure that the pipe is buriedsuch that any external load, such asthe weight of the soil, or vehiculartraffic does not cause the verticaldimension of the pipe to flatten bymore than 5%. Suggested procedure is to pressurize before backfilling tominimize flattening of the pipe. Allinstallation should be in compliancewith local codes. Additional informa-tion on trenching and pipe embedmentpractices can be obtained from ASTMD2774, Standard RecommendedPractice for Underground Installationof Thermoplastic Pressure Piping, or the American Water WorksAssociation (AWWA) report TR31,Underground Installation of Poly-olefin Piping.


Installation PrecautionsProtect RadiantPEX Tubing atExpansion Joints.If RadiantPEX tubing is installedunder expansion joints, the pipingmust be either sleeved with a protec-tive layer of insulation, or the pipingmust dip under the slab into the under-lying base material. See elsewhere inthis manual for further details.

Avoid Excessive Pressure andTemperature.RadiantPEX is rated up to 160 psi at73°F, 100 psi at 180°F, or 80 psi at200°F. Make sure you don’t exceedthese temperature and pressure ratings.Exceeding rated temperature or pres-sure will void the warranty.

Protect From Sharp orAbrasive Hangers.RadiantPEX can be damaged by metalhangers with sharp or abrasive edges;don’t use them. Don’t use hangers, staples, or fasteners that crush or pinchRadiantPEX pipe. Be careful whenusing hangers or fasteners. Make surethey are not driven in too far and damage the pipe. Better yet, useapproved Watts Radiant fasteners.

Protect from Excessive Heat

RadiantPEX must be protected againstexcessive heat. Following are sometypical kinds of exposure to excessiveheat that you must be careful about.

Soldering.Never solder next to RadiantPEX. Ifyou are soldering onto a RadiantPEXfitting, make the solder connectionfirst and then make the connection tothe RadiantPEX second.

Water Heaters and Boilers.Use metal tubing to transition betweenwater heaters and RadiantPEX.Maintain a minimum of 18" separationbetween the RadiantPEX and waterheaters/gas boilers.

Recessed Light Fixtures.Maintain at least 12" of separationbetween all recessed light fixtures andthe RadiantPEX tubing.

Gas Appliance Vents.Maintain at least 6" of separationbetween RadiantPEX and all gasappliance vents. Maintain at least 18"of separation between RadiantPEXand wood appliance vents.

Protect from Chemicals

Chlorine.Except for short-term superchlorina-tion of potable water lines when apotable water system is being cleaned,do not permit prolonged exposure offree chlorine concentrations in excessof 2 parts per million. Do not exposeRadiantPEX to any chemicals internally or externally, other thanwater or water/glycol solutions, unlessapproved by Watts Radiant.

Leak-Testing Agents.Certain kinds of chemicals found inliquid-based leak detectors, especiallythose containing soap, can causelongterm damage to PEX and othertypes of plastic pipes. The same chemicals used to “lift” dirt fromsoiled clothes can cause microfractur-ing of PEX pipe and lead to its eventual failure.

Adhesive Tape.RadiantPEX can also be damaged by some of the adhesives found inadhesive tape. Unless an adhesive tape or label is supplied by a PEXmanufacturer do not apply adhesivetape to any PEX.

Pipe Dope, Threading Compound,Mineral or Linseed Oil.RadiantPEX is damaged by some ofthe materials found in pipe dope, mineral oil, putty, cutting oil, and similar compounds. Do not exposeRadiantPEX to these materials.

Petroleum Products.RadiantPEX is damaged by petroleumproducts such as gasoline, diesel fuel,cutting oil, brake and transmission fluids, and others. Do not exposeRadiantPEX to these materials. Do notbury RadiantPEX in soil that is contaminated with these materials.

Do not use RadiantPEX to convey natural gas, propane, fuel oil, or anyother hazardous or volatile fluids. Do not use RadiantPEX as an electrical ground.

Protect Against Freezing

While RadiantPEX is resistant tofreeze damage, we recommend that all systems be protected from freezingin a manner typical of the area.RadiantPEX cannot prevent damage to materials if the system freezes.RadiantPEX fittings and field connec-tions can be damaged if a system isallowed to freeze.

Handling and Care ofRadiantPEX

Storage of Pipe.Reasonable care and protection mustbe taken to protect RadiantPEX fromdamage, both before and during theconstruction process.

Temperature Range.Caution should be exercised wheninstalling RadiantPEX at temperaturesbelow freezing. The pipe is more easily damaged and kinked wheninstalled at these temperatures. Bestresults are observed when the pipe isinstalled at temperatures above 50°F.In very cold weather you may wish to warm the pipe up in a heated room or truck cab before installing it.RadiantPEX is most flexible wheninstalled at temperatures above 50°F.


Installation PrecautionsReforming Kinked Pipe.1. Gently straighten the kinked

RadiantPEX.

2. Using an electric heating gun, gently heat the kinked area using a sweeping motion of the heat gun that is parallel to the kink, and perpendicular to the pipe. Neveruse any type of open flame.

3. Maintain at least 1" of distance between the end of the gun and the surface of the pipe. Do not holdthe nose of the heat gun against the pipe or allow the nose of the heat gun to come in contact with the pipe.

4. Do not overheat the kinked area in an attempt to speed up the process. The surface temperature should not exceed 265°F. The hot air from the gun should not exceed 350°F. If the gun you are using is rated at a higher temperature, hold it back further from the pipe.

5. Within a minute of heating, the tubing should gradually begin to straighten and return to its original shape. Any small creases in the kink should begin to fade.

6. As soon as the pipe returns to a generally round shape and the kink has smoothed out, stop heating it. The pipe should not be discolored.

7. Do not disturb the pipe until it cools down to room temperature.

8. Before burying the pipe it must be pressure tested.

Thawing Frozen Pipes.RadiantPEX pipe is somewhat resist-ant to freeze damage, but can be damaged by excessive heat. For thatreason please follow these precautionswhen thawing frozen pipes.

Do not attempt to send electrical currents through the pipe to melt theice. Do not apply a torch to the pipe’sexterior.

You can use hot air guns, as long asthe temperature of the air does notexceed 300°F. Do not apply heat fromhot air guns for more than 5 minutes at a time to one spot on the pipe. Donot heat the pipe to the point where itbegins to change color.

Splicing Damaged Pipe.If at all possible, don’t make splices in inaccessible locations, such as under slab floors, or behind dry wall. If it is necessary to make buried splices, wrap the field coupling with insulation to protect the metal compo-nents against possible corrosion and mechanical stress. Pressure test splices before burying. Use only genuine RadiantPEX field repair kits when making these field splices. Never use any hose fittings/clamps or non-RadiantPEX fittings/clamps when making splices or connections.

Sunlight Exposure.Do not expose RadiantPEX to morethan 30 days of direct sunlight. It willdamage the pipe and void the warranty.


The Design Process

A system design should be performedfor all radiant projects. This designshould include, at minimum, a radiantheat loss calculation, minimum tubingrequirements and pump size calcula-tions.

Watts Radiant’s RadiantWorks® designsoftware should be used to account for all building specifications and allsystem components. A copy ofRadiantWorks can be obtained throughyour local Watts Radiant representa-tive. A demo version of the programcan be downloaded from our website:www.wattsradiant.com.

Keep in mind, conventional heat losscalculations will tend to over-estimatethe actual heat loss that a radiantbuilding experiences. In this manual,the design steps and the report exam-ples shown are from Watts Radiant’sRadiantWorks design software.

Should additional information aboutdesign, controls or other radiant appli-cations be required, please call yourlocal Watts Radiant representative orthe Watts Radiant design departmentfor assistance.

Step 1: Initial DesignConsiderations

There are three primary considerationsin a radiant design.1. Heat Loss — how much energy

do we have to impart to the system to keep the occupants warm or the surface snow and ice free?

2. Tubing — how much and what type of tubing is required to deliver the needed heat?

3. Control and Performance —system operation will vary greatlydepending on how the system iscontrolled and operated.

To answer these questions, some initialinformation is needed. This informa-tion primarily relates to the heat losscalculation. It is important to gather as much project information as possi-ble. Even though this information isconveyed to the end user via theRadiantWorks Assumption Report, itsaves time and effort to have the correct information at the beginning.

To perform an accurate heat loss andradiant design, the following informa-tion is required.

Heating:1. Wall R-Values2. Ceiling R-Values3. Window R-Values and Sizes4. Amount of exposed wall5. Fireplaces or other high

infiltration sources, such as overhead hoods and vents

6. Floor Cross Section: It is important to know how many separate layers make up thefloor. Different floor coveringsmay have anywhere from one tofour distinct layers

7. Finish Floor Covering Materials8. General Site Information

Snowmelting:1. Slab construction details2. Amount of snowfall3. Desired response time4. General Site Information

Additional information concerningsnowmelting systems is discussedin the Snowmelting section.

Floor Coverings

The main misconception regardingfloor coverings tend to center onwhether or not carpet or wood can beused over a radiant floor.

Virtually any floor covering can beused if the insulative value (R-value)for that covering is accounted for inthe radiant design and installationprocess. In a radiant floor heating system, the floor is the room’s heatsource. The floor gives off heat (energy) to the room because it iswarmer than the surroundings — hotmoves to cold. If we want to maintaina room temperature of 70°F, the floorhas to be warmer than 70°F. Thewarmer the floor, the more energy itwill emit into the space. So, the higherthe heating load, the warmer the floorneeds to be. The room does not carewhat the floor type is, or what the construction details are as long as the

Floor Coverings

Carpet and pad generally requires

the highest supply fluid

temperature.

Hardwoods are themost popular floor

covering to use over a radiant floor system.

Tile and other stone floorcoverings generally

require the lowest supplytemperature. The more

conductive the floor covering the lower therequired supply water

temperature.


required floor surface temperature is achieved.

There is a limit to how hot we canmake the floor. In theory, we couldheat any room with the use of a radiant floor heating system. The limiting factor is human comfort. Themaximum temperature we can allowthe floor surface to reach is 85°F.Temperatures above this point becometoo warm for our bodies and in turnmake the floor uncomfortable to standon. This 85°F floor limit in turn limitsthe maximum BTU output of the floorto around 45 BTU/sq.ft., based onroom temperature.

With this in mind, let’s return to thefloor itself and look at the differentfloor coverings. All floor coveringshave different conductivity values.Conductivity values relate a material’sability to transfer energy. The higherthe conductivity, the better the materialconducts, or transfers energy. Forexample, wood has a conductivityvalue of approximately 0.078 BTU/hr/ft/°F while tile has a conductivity of 0.41 BTU/hr/ft/°F. In this example,tile will transfer energy faster. Butdoes that make tile a better choice?Not really. Both the hardwood floorand the tile floor will perform exactlythe same if we maintain the same surface temperature. To do this, wehave to vary the supply water tempera-ture depending on the floor coveringand construction. A hardwood floormay require 120°F supply temperaturewhile a tile floor may only require100°F.

Even though the main goal is the same for all floor types, there are some special considerations that needto be maintained for each floor cover-ing. The following should be used as a guide only. If more information is required, contact the flooring manu-facturer for more specific informationrelative to the actual floor coveringbeing used.

Tile Floors

Tile, stone, and other masonry floorsare unique in the sense they are bond-ed to the main floor construction. Inaddition, they are extremely hard and,to some degree, brittle. Hard surfacesrequire special care during the installa-tion process, whether or not a radiantsystem is being installed.

Some items to be aware of are:

1. Floor stability. Tile will crack if the floor has a deflection greaterthan 1/360th of the span. To mini-mize this deflection, adequatejoists, subfloor, and a stiffeninglayer such as a tile backer board oradditional plywood, may beinstalled over the subfloor.

2. Crack/Isolation Membrane. Floors move continuously overtime as the environment changes.Tile installed over a slab or a framefloor is subject to crack propaga-tion as the slab below developsminor cracks or as the subfloorshifts. A cleavage membrane or a crack/isolation layer is recom-mended to prevent cracks frommoving upward through the tile.

3. Mortar and Adhesives. There are a wide range of mortarsand adhesives used with tile andstone. Most standard mortar andlatex modified thin-sets are ade-quate for tile and stone applicationsover radiant.

As with any cement or mortar floor-ing, DO NOT apply heat to the sys-tem until the flooring materials havehad time to cure. This usually takesanywhere from 14 to 28 days.

Hardwood Flooring

Watts Radiant customers have success-fully installed parquet, laminated, andstrip wood flooring over radiant tubingfor decades. Most wood floor manu-factures limit the floor surface temper-ature to 85°F. Since the radiant designuses the same surface temperaturelimit, hardwoods can be used in almostany room or application with a radiantfloor.

This is not to say certain precautionsshould not be followed. These instal-lation techniques are the same fora radiant floor heating system asthey are for a conventional forcedair system.

Wood Moisture Content

Wood is hydroscopic, meaning it actslike a sponge. If the wood is installedwet relative to its surroundings, it willgive off the excess moisture and

Typical tile/stone installation sequence over aframe floor.

Plywood Subfloor

Thin set

Backerboard

Tile Thin setTile/Stone Covering

Typical hardwood installation sequence over aframe floor.

Plywood Subfloor

Felt Paper (tar free)

Hardwood/Laminate Floor Covering

Floor Coverings


shrink. If the wood is installed dry rel-ative to its surroundings, it will absorbmoisture and expand. We all haveexperienced this within our ownhomes. The back door seems to fittighter in the summer than it does inthe winter. This is because the humidi-ty levels are higher in the summer. Thewood absorbs this excess moisture andexpands. A wood floor will do thesame thing. This is the reason why a1/2" to 3/4" gap is placed around theperimeter of the room.

On average, wood can expand or con-tract within 7% of its original size. Fora single planking of wood, this canequate to as much as 1/8" in width. Tohelp minimize this effect, a few guide-lines have been developed to reducethe effects moisture can have on awood floor.

1. The wood must be kiln dried. Kiln dried wood ensures the core ofthe wood is at the same moisturecontent as the outer surface

2. Hardwood Moisture Content.Wood is naturally stable between7% and 10% moisture content.

3. Subfloor Moisture Content. Make sure the moisture content ofthe subfloor is no higher than 4%above the hardwood itself. If it is,then moisture can be driven fromthe subfloor to the hardwood, caus-ing its internal moisture levels tochange.

4. Concrete Moisture. Make sure the concrete slab below the hardwood has a vapor barrier toprevent absorption from groundmoisture. Make sure to test that theconcrete has completely dried beforeinstalling hardwood floors.

5. Room Moisture. Try to keep the room’s relativehumidity between 35% and 50%moisture.

6. Use Strips, not Planks. The narrower the board, the less movement it will create. The idealmaximum size is 3" to 3-1/2" inwidth.

7. Quarter Sawn vs. Plane Sawn.Quarter sawn wood will expand inheight while plane sawn wood willexpand in width. A quarter sawnboard is more dimensionally stablethan a plane sawn board.

Controlling Moisture

The most common cause of moistureproblems in a new home is moisturetrapped within the structure duringconstruction. Problems sometimesarise from a continuing source ofexcess moisture, e.g., from the base-ment, crawl space, or slab.

For a slab on or below grade, a mini-mum 6 mil plastic vapor barrier shouldbe used under the slab to prevent theabsorption of ground moisture through

the concrete during the non-heatingseason. Verify with local code andbuilding practices.

Before wood flooring is installed overany slab or elevated thin slab, the slabshould be well aged. Preferably, theslab should have been heated for atleast a week before the flooring isdelivered. Pre-heating the slab beforeflooring installation will drive outresidual moisture that might causeproblems. This pre-heating must bedone before a surface vapor barrier isinstalled.

There is a simple procedure for check-ing the presence of excessive moisturein the slab. Tape a 4' x 4' section ofpolyethylene plastic sheeting to thesurface of the slab and turn on theheat. If moisture appears under theplastic, the slab should be heated foranother day or so and then checkedagain for moisture. If a hardwood flooris to be laid over a wooden subfloor,similar precautions should beobserved, as the plywood subfloormay also be saturated with moisture.

The recommended procedure is to firstdrive off the moisture in the slab, thenheat the plywood subfloor for a few

Standard slab on grade construction

Without a vapor barrier: mois-ture moves through a slab viacapillary movement.

With a vapor barrier, mois-ture is prevented fromentering the slab.

Movement for 3" wood strip.

% Moisture Approx. WidthChange Change/Inch

1 1/128"4 1/32"8 1/16"12 5/64"16 7/64"20 9/64"24 11/64"

Potential Shrinkage

Installed Dimension

Potential Expansion

Hardwood expansion.

Floor Coverings


days before unwrapping the finishflooring from its factory packaging.

Plywood or oriented strand boardmake good candidates for subfloormaterials in radiant installations. Donot use particle board as a subfloor.

USDA Forest ServiceRecommendations

The following procedures are recom-mended by the USDA Forest Service’s“Wood Handbook.”

Cracks develop in flooring if (thewood) absorbs moisture either beforeor after it is laid, and then shrinkswhen the building is heated. Suchcracks can be greatly reduced byobserving the following practices:

1. Specify flooring manufactured according to association rules and sold by dealers that protect it properly during storage and delivery.

2. Do not allow the flooring to be delivered before the masonry andplastering are completed and fullydry, unless a dry storage space isavailable.

3. Have the heating plant installed before the flooring is delivered.

4. Break open the flooring bundles and expose all sides of the flooringto the atmosphere inside the structure.

5. Close up the house at night andraise the temperature about 15°Fabove the outdoor temperature for3 days before laying the floor.

6. If the house is not occupied imme-diately after the floor is laid, keepthe house closed at night or duringdamp weather and supply someheat, if necessary, to keep thehouse at about 65°F.

Cautions for HardwoodFloor Installations:

If the radiant heating system cannot beinstalled prior to the hardwood instal-lation, an alternative form of heat

needs to be provided while the floor isbeing installed. Temporary, unventedsources of heat (such as a propanefired “salamanders”) are not appropri-ate as they can put excessive amountsof water vapor into the building.

Asphalt paper should never be usedwhen installing a radiant floor heat-ing system, as it may give off anunpleasant odor when it is heated. If indoubt as to the presence of old asphaltpaper when doing a building renova-tion, a floor core sample needs to betaken. Watts Radiant does not recom-mend radiant installations underasphalt paper.

As a rule of thumb, standard 3/4"hardwood floor coverings with a 3/4"subfloor do not pose a problem to normal heat transfer. The performanceof a radiant floor begins to be affectedwhen the total thickness of wood

The National Hardwood Council allows the hardwood to be installed directly on top of the radiant tubing.However, it is advised to first install a subfloor over the radiant system, or use C-Covers, to help protectthe tubing from nails and other attachment devices.

PlywoodSubfloorRadiantPEX

C-Cover

JoistJoist

HardwoodFloor Covering

Wood Sleeper

Wood Sleeper

RadiantPEX

Slab

Earth

Floor Coverings

Caution should be taken whenselecting flooring nail sizes andinstallation locations. Use a floor-ing nail that will not penetratepast the subfloor.

Foil-FacedBatt insulation

HardwoodFloor Covering

C-Cover


covering is between 2"–3". This rangeis dependent on the heating intensity.Lower heating intensities allow forthicker wood coverings.

There is added caution for wood floorswhen installed in a Sandwich applica-tion. The National Hardwood Councilallows the hardwood to be installeddirectly on top of the radiant tubing.However, it is advised to first install a1/2" or 3/4" subfloor over the radiantsystem, or use C-Covers, to help pro-tect the tubing from nails and otherattachment devices.

It is important to note that the floorconstruction above the tubing needs to be continuous, i.e., no air gaps. Airgaps will increase the floor’s overallR-value, thus reducing the floor’s ability to transfer energy, which will inturn decrease performance.

Carpet and Pad Flooring

Carpet floor coverings help preventfloors from feeling cold because theyhave a higher R-value, or resistance toheat transfer, than any other floor cov-ering. Carpet pads reduce energytransfer while providing some supportand cushion to those standing.

With respect to a radiant floor heatingsystem, a carpet and pad floor cover-ing is the most difficult to heatthrough. In general, the ideal floorcovering would have an R-value of 2or less. In most cases, since we areusing a floor heating system, a thinnerpad should be used. Try to keep thepad thickness below 1/2".

Step 2: Radiant Zoning

Zoning is a way of controlling howheat is delivered to a given area. Themore zones there are, the higher thecontrol level. There is no “rule” to theamount of zones needed for a project.There can be as many zones as thereare rooms and as few zones as thereare floor levels (minimum one zoneper floor level). There are severalways to zone a project.

1. Zoned by Floor Coverings:Different floor coverings transferenergy at different rates, resulting invarying supply water temperatures.A kitchen with a tile floor may only need 100°F supply water, while the family room right next toit with a carpet may require 140°Fsupply water. If these two roomswere placed on the same zone, there may be control and comfortproblems.

2. Zoned by Occupancy: Different areas of a home or busi-ness will be used during differenttimes of the day or for differentactivities. Bedroom or warehouseareas tend to be kept at a lower ther-mostat setting while the rest of abuilding will tend to be keptwarmer.

3. Zoned by Construction: There are various construction details present in almost every project. For example, it is difficult to place a room with a slab floor onthe same zone as a room with aframe floor. Likewise, it is a goodidea not to zone multiple levels of aproject on a single zone. Tubing isnot easily installed from one level tothe next and heat losses/gains can bedramatically different from floor tofloor. Other construction concerns

Carpet Type Thickness (in) R-ValueLevel Loop . . . . . . . . . . . . . . . . . . . . .0.26 . . . . . . . . . . . . . .0.64Berber . . . . . . . . . . . . . . . . . . . . . . . . .0.41 . . . . . . . . . . . . . .0.83High/Low Loop . . . . . . . . . . . . . . . . . .0.42 . . . . . . . . . . . . . .0.86Berber . . . . . . . . . . . . . . . . . . . . . . . . .0.42 . . . . . . . . . . . . . .0.96Berber . . . . . . . . . . . . . . . . . . . . . . . . .0.48 . . . . . . . . . . . . . .1.00Frise . . . . . . . . . . . . . . . . . . . . . . . . .0.42 . . . . . . . . . . . . . .1.10Saxony . . . . . . . . . . . . . . . . . . . . . . . .0.41 . . . . . . . . . . . . . .1.10Saxony . . . . . . . . . . . . . . . . . . . . . . . .0.44 . . . . . . . . . . . . . .1.15Saxony . . . . . . . . . . . . . . . . . . . . . . . .0.50 . . . . . . . . . . . . . .1.25Saxony . . . . . . . . . . . . . . . . . . . . . . . .0.55 . . . . . . . . . . . . . .1.32

Cushion Thickness (in) R-ValueSlab Rubber . . . . . . . . . . . . . . . . . . . .0.23 . . . . . . . . . . . . . .0.62Waffled Sponge Rubber . . . . . . . . . . .0.43 . . . . . . . . . . . . . .0.78Prime Urethane . . . . . . . . . . . . . . . . .0.40 . . . . . . . . . . . . . .1.61Hair and Jute Coated . . . . . . . . . . . . .0.44 . . . . . . . . . . . . . .1.71Bonded Urethane . . . . . . . . . . . . . . . .0.50 . . . . . . . . . . . . . .2.09

Carpet and Pad Combined Thickness (in) Total R-ValueLevel Loop and

Textured Rubber . . . . . . . . . . . . . . .0.36 . . . . . . . . . . . . . .1.04Level Loop and Froth . . . . . . . . . . . . .0.25 . . . . . . . . . . . . . .1.23Berber and Textured Rubber . . . . . . .0.36 . . . . . . . . . . . . . .1.36Berber and Froth . . . . . . . . . . . . . . . .0.25 . . . . . . . . . . . . . .4.54Saxony and Textured Rubber . . . . . . .0.36 . . . . . . . . . . . . . .1.62Level Loop and

Bonded Urethane . . . . . . . . . . . . . .0.32 . . . . . . . . . . . . . .1.67Level Loop and

Synthetic Fiber . . . . . . . . . . . . . . . .0.33 . . . . . . . . . . . . . .1.67Saxony and Froth . . . . . . . . . . . . . . . .0.25 . . . . . . . . . . . . . .1.83Level Loop and

Grafted Prime . . . . . . . . . . . . . . . . .0.36 . . . . . . . . . . . . . .1.88Berber and Synthetic Fiber . . . . . . . . .0.33 . . . . . . . . . . . . . .1.98Berber and Bonded Urethane . . . . . .0.32 . . . . . . . . . . . . . .2.01

Typical carpet and pad installation sequence overa frame floor.

Floor Coverings

Subfloor

Carpet Pad

Carpet


might be varying joist directions orexpansion joint locations.

4. Zoned by MechanicalConsiderations: Mechanical issues tend to relate tothe required supply water tempera-ture or heat load required in a givenarea.

Typically, rooms can be grouped in the same zone if the supply water temperature does not cause the floorsurface temperature in any of therooms to exceed 85°F.

Rooms with similar heating intensities(BTU/sq.ft.) can be zoned together, as well. If a room has a load of 50 BTU/sq.ft., like a sunroom, itshould not be zoned with a room thatonly requires 10 BTU/sq.ft.

The above illustration uses the occu-pancy technique for zoning, dividingthe “waking” areas from the “sleep-ing” areas.

Subzones are areas within a zone withdedicated runs of tubing. In the houseillustration, the master bathroom is asubzone of the master bedroom. In thiscase, there are five circuits for thiszone. Three circuits are dedicated tojust the master bedroom while two cir-cuits are dedicated to just the masterbathroom. If the master bathroom werenot designated a subzone, all circuitswould be installed in both areas.

Subzones can be used to help balancethe heat delivered within a zone. By

designating certain circuits to specificareas, heat delivery can be controlledby flow (circuit balancing valves ortelestats).

Step 3: Manifold Location

Each zone has one manifold pair: asupply and a return. Watts Radiantoffers a wide range of manifolds rang-ing from custom brass and cast brassto stainless steel manifolds. Moreinformation on manifold options canbe found in the Watts Radiant productcatalog or on the Web site.

With respect to any design, the mani-fold location has a direct impact notonly on the aesthetics of a room, butalso on the amount of tubing beinginstalled.

1. Manifolds should be placed in alocation that allow them to remainaccessible, but also out of sight. Incabinets, behind doors, and in clos-ets are good locations. These loca-tions allow for the use of a coverplate or manifold box over themanifold to keep the assembly hidden from everyday view.

2. Manifold placement determines the minimum tubing circuit length.Minimum circuit equates to the distance from the manifold to thefarthest point, taking right angles,and back. For most residential projects, 200' circuits are adequate.For most commercial projects,300'–400' circuits are used.

Supply/Return Piping

Supply Max. Flow Pipe Size Rate (typical)

3/4" 4 GPM1" 12 GPM

1-1/4" 20 GPM1-1/2" 32 GPM

2" 60 GPM

ZONE 1

SUBZONE 2A

ZONE 2

Typical radiant zoning.

Zoning


3. Locate the manifold within the given zone. If a manifold is locatedoutside the zone boundary, thentwice the distance (supply andreturn) to the manifold needs to be added to each circuit length. Forexample, if a zone calls for 180'.circuits, and the manifold is movedto a location 10' away, then 20' isadded to the circuit. The circuitlengths required for this zone willbe 200'.

4. Manifolds should be mounted horizontally if a vent/purge assem-bly is installed. This allows for easier circuit connection to themanifold, and allows the vents towork properly without leaking.

5. Manifold sizes are based on the zone flow rates (GPM). The smallest trunk size provided by Watts Radiant is 1". For commer-cial and snowmelt applicationslarger manifolds, 1-1/4" to 6" ID,are available.

Step 4: Heat Loss Calculation

Conventional heat loss calculationscan be used to size radiant heatingequipment; however they tend to overstate the actual heat loss that aradiantly heated building experiences.In addition, the use of these unadjustedcalculations will tend to oversize boilers, circulators, and piping, as wellas the amount of radiant pipingrequired. There are four major factorsthat reduce heat loads as compared toconventional heating systems.

1. Lower indoor air temperatures can be maintained for greater human comfort. When the floor is

Zoning

Floor Covering

Bend Support

Manifolds

Bend Support

Joist

Manifold Trunk Sizing

Manifold Flow Manifold Max. GPM Trunk Size

12 1"20 1-1/4"32 1-1/2"60 2"


radiantly warmed, the human bodydoes not need as warm an air tem-perature to stay comfortable. Withradiant heat, the indoor thermostatcan be set 2°–3° lower.

2. Indoor air movement and tempera-ture gradient is greatly reduced. This reduces heat loss through the ceiling.

3. Because of factors one and two,infiltration losses are also less. Thismeans buildings with higher airinfiltration rates will save moreenergy if fitted with a radiant floordelivery system, compared to aforced air (convective) heating system.

4. Due to heat storage in the radiantfloor and surrounding walls, peakheating loads are reduced. Thiseffect is greater in more massiveconstruction.

Due to these factors, a typical radiant-ly heated building often requires 10–30% less energy to heat than aconventional convective system.RadiantWorks automatically accountsfor these factors to properly and accurately size any radiant project.

Using RadiantWorks®

Reports as a Design Tool

For most projects, the radiant designwill be performed using WattsRadiant’s RadiantWorks design soft-ware. This is an easy, efficient way toapply the design steps discussed earli-er. A variety of reports are availablethrough RadiantWorks, including aZone List, an Assumption report and aHeat Loss report. These reports helptransfer information about a projectquickly without guess work.

Zone List ReportEach Zone List contains informationon what is required to properly heat agiven area. It is important to verifythat the Radiant Capacity for eachroom within a zone is greater than the

ZONE 1 - MAIN LEVEL (Under-Floor)

Room SpecificationsRoom Name Primary

Spacing[in]

PrimaryArea[ft]

BandedSpacing

[in]

BandedArea[ft]

HeatingIntensity[Btu/h ft]

RequiredHeat

[Btu/h]

RadiantCapacity[Btu/h]

Foyer 8 118 --- --- 15.7 1,853 2,421Powder Room 8 42 --- --- 27.2 1,144 1,147Breakfast / Kitchen / Family / Pantry

8 520 --- --- 17.2 12,012 13,832

Hall 8 135 --- --- 16.0 2,154 2,484

Zone SpecificationsSupply

Fluid [°F]Delta T

[°F]GPM Head

[ft]RadiantPanelLoad

[Btu/h]

ProductType

TubeLength [ft]

No. ofCircuits

112 20 2.4 2.1 24,038 1/2" PEX 300 8Pump Specs & Radiant Panel Load are calculated on the smaller ofRequired Heat or Radiant Capacity (+ back and edge losses)

Project Assumptions

OutsideTemp [°F]

Elevation[ft]

WindSpeed[mph]

Glycol Job Type SystemChemicals

0 1268 10 None Residential No

ZONE 1 - MAIN LEVEL (Under-Floor) [3/8" RadiantPEX]

Min Tube Length: 20 ft Max Tube Length: 300 ft Circuit Rounding: 5 ftSupply Water Temp:

112.3°F Delta T: 20°F Manifold Distance: 0 ft

Joist Spacing: 16 in Joint Thickness: 1.5 in Joist Conductivity: 0.078 Btu/h-ft-F

Subfloor Thickness: 0.75 in Subfloor Conductivity:

0.085 BTU/h-ft-F

FoyerRoom Size Parameters:

Area: 118 ft Perimeter: 44 ft Total Area: 118 ftHeated Floor Area: 118 ft Unheated Floor

Area:0 ft

Room Construction Parameters:Space Below: Crawl

SpaceCrawl Space Insulation:

Yes

Foil Faced Insulation Thickness:

3.5 in Tube Spacing: 8

Room Heat Loss Parameters:Indoor Design Temp:

68°F Max Eff. Surface: 85°F Heating Intensity: 15.70 Btu/h ft

Floor Covering: Tile Floor & Mudset

R Value: 0.16 Unheated Floor R Value:

19

ACH: 0.5 CFM: 7.867 Number of Stories: 1Ave. Ceiling Height:

9 ft Exp'd Ceiling Area: 118 ft Ceiling R Value: 30

ZONE 1 - MAIN LEVEL (Under-Floor)

Calculated Heat Loss for Foyer @ 68°F IndoorDescription Units R-Value Heat Loss

[BTU/hr]Infil. Loss[BTU/hr]

Total Loss[BTU/hr]

Exposed Walls 59 ft 13 303 0 303Doors 21 ft 2 635 0 635Exposed Ceiling Area 118 ft 30 265 0 265Infiltration 0.5 ACH 650 650Totals 1203 650 1853

ApplicationsRadiantWorks Zone List Report

RadiantWorks Assumption Report

RadiantWorks Heat Loss Report


Required Heat. If this is not the case, then the room will require auxiliary heat.

Assumption Report The Assumption Report conveys infor-mation about the heating system tothose working on the project. It showsall of the assumed values and condi-tions taken from a plan or blueprintwhen calculating the heating load for a project.

Many projects change during the con-struction process. Windows get addedto the living room, a fireplace is addedto the family room, etc. Hardwoodreplaces carpet or a skylight goes intothe master bathroom. Sometimes,these changes happen after the initialradiant design is done. Although thesechanges seem small and inconsequen-tial, they can have a drastic impact onhow a radiant floor heats a space.

If the window size for the family roomgoes from 30 sq. ft. to 50 sq. ft., theheat loss through that section of walljust increased over 60%! This seem-ingly simple change might requiremodifications to the radiant heatingsystem, such as additional banding(tighter tube spacing along an exposedwall, where applicable) or higherwater temperatures and possibly alarger heat source.

Heat Loss ReportThe Heat Loss Report is a room-by-room breakdown of exactly whereenergy is lost. This information is usedto identify those items that are causingan unusually high heating load. Forexample, assume the load for a roomwas 10,000 BTU and the assumedwindows were single pane and had atotal heat loss of 6700 BTU. The HeatLoss Report would reflect this unusu-ally high heat loss area and a decisionto install double pane windows mightbe made to help make this room moreenergy efficient.

Applications

It is impossible to try to fit all possible construction scenarios intothis manual. Because of this, only themost common applications are discussed. Each section containsexamples and techniques for the most popular variations.

Should a project call for a constructiondetail not mentioned in this manual,please feel free to contact WattsRadiant or a Watts Radiant representa-tive for design assistance.

Frame Floors

Introduction Even though some installation detailsvary from application to application,basic design considerations remain thesame. The most important goal is tomake sure the RadiantPEX is installedin accordance with the design parame-ters. If not, the system may not func-tion as desired.

Frame Floor Applications

Supply/Return Manifold

Subfloor

Heat Transfer Plates

Joist

RadiantPEX

Foil FacedInsulation

LockDownSuspension Clips

Typical UnderFloor Application

The second most important detail foran UnderFloor application is to prop-erly install foil-faced batt insulationbelow the tubing. If a non-foil-facedinsulation is used, the system mayoperate with a 25% loss of maximumheat output and some (smaller) lossof efficiency. Other insulation can beused instead of a fiberglass batt, how-ever, certain cautions need to beobserved.

1. Tight seal. One of the largest areasof heat loss with any underfloorapplication is convective lossthrough the band joists and otherperimeter areas. The tighter thejoist cavity, the better the systemwill perform. This joist cavity mustbe sealed with insulation along thejoists and at the perimeter. Also,any electrical, plumbing, or otherpenetrations into the heated joistbay must be sealed with insulationor caulk.

2. Foil Face. The foil on the insula-tion will ensure most of the heatcoming from the tubing is reflectedup to the subfloor where it is dis-tributed. This foil also spreads theheat out over the subfloor, reducingtemperature variations.


3. Air Gap. A 2"–4" air gap is neces-sary between the tubing and theinsulation. This air gap helpsincrease the effective R-value ofthe insulation while fully optimiz-ing the ability of the foil insulation.If contact is made, energy is nolonger reflected upwards, butrather, is conducted downward.This can reduce the effective heating of the floor by 10–20%,depending on the load conditionsand thickness of insulation.

4. R-Value. As a rule of thumb, anR-Value of at least 4 times higherthan the floor is desired. For mostindoor conditions, an R-13, or a 3-1/2" batt should be used. Wheninstalling over an unheated area,exposed area or crawlspace, a minimum R-19 or 6" batt should be used.

Design Parameters

With any new or renovation project, itis important to know the layers used inthe floor construction. As these layersincrease or change, variances in theheating system will result.

RadiantPEX SpacingRadiantPEX is generally installed 8"on center, to the underside of the sub-floor for an UnderFloor application.Closer spacing may be used in areas ofhigh heat loss, such as an exposed wallwith a high percentage of glass.Tighter tubing spacings, up to 4" OC,may also be used in areas that have alow thermal conductivity, such asareas with thicker than normal sub-floor or dense carpet and pad.

Note: Tighter than 8" OC tube spacing is only possible if 3/8" PEXis used. If 1/2" PEX or larger is usedon the project, the design shouldmaintain a constant 8" OC spacing.

It is important to note that simply doubling the amount of tubing doesnot double the floor’s heating output.The floor’s ability to deliver heat to aroom is based on the temperature difference between the floor and theroom. The amount of radiant tubingand the fluid temperature control thefloor surface temperature.

RadiantWorks design software gener-ates a specific Nomograph for eachroom. Nomographs are charts thatdetail key factors associated with aroom, such as tube spacing, floor surface temperature, floor heatingintensity, mean (average) water tem-perature and back and edge losses.Nomographs are essential to any radiant design. More information onhow to read and use a Nomograph can be found in the Appendix.

Frame Floor Applications

Suspension Clip

4" OC RadiantPEX spacingfor a distance of half

the wall height.8" RadiantPEX Spacing

Banding Areas. RadiantPEX is sometimes installed at closer spacings at the perimeter of exteriorrooms to improve comfort.


Subfloor

Upper Subfloor

Joist

RadiantPEX

Foil-faced Insulation

Finished Floor Covering

Heat Transfer Plate and Sleeper


UnderFloor Application

Installation Methods

When considering a RadiantPEXUnderFloor application it is importantto first determine the type ofUnderFloor system to use. There aretwo primary methods of installing an

UnderFloor system — with heat trans-fer plates and suspended.

Why the two methods?These two techniques for installingPEX tubing in underfloor applicationshave emerged due to the movement ofPEX as it heats and cools. This move-ment can lead to noise, as well asreduced heat transfer. As mentionedbefore, PEX will expand and contractin length based on the change in tem-perature. Given the correct conditions,this can be as much as 33" per circuit.

PEX used to be installed in a similarmanner as Watts Radiant’s Onix tubing, that being stapled directly tothe underside of the subfloor. Unfortu-nately these systems proved to benoisy. As the PEX expanded and con-

tracted, it would move across the sur-face of the subfloor, creating a “tick-ing” or “popping” noise which provedto be annoying and could possibly leadto pipe damage at the staples.

In response to this, methods weredeveloped to minimize the noise whilecontinuing to deliver the required heatload to the space.

Heat Transfer PlatesHeat transfer plates are aluminumplates that are either roller or extruded.Watts Radiant offers an aluminumplate designed to be used with 1/2"Watts Radiant RadiantPEX.

Do not use these plates for any PEXsizes other than 1/2".

The heat transfer plate is attached tothe subfloor and the RadiantPEX isthen inserted into the plate. Thisallows the PEX to be separated fromthe subfloor, eliminating the noiseissue before mentioned.

However, this separation raises concerns relative to the conductivetransfer of energy needed to deliverthe required heat to a space. The aluminum transfer plates offer thiscontact, allowing for conduction tocontinue from the RadiantPEX to the subfloor.

In most cases a PEX system installedwith heat transfer plates will stilldeliver the required BTU load to aspace. The maximum BTU deliveredwill typically be around 45 BTU/sq.ft.

It is important to install the aluminumplates in accordance with the specifiedinstallation details. Failure to do somay result in noise associated with the aluminum plates moving duringthe heating process. Refer to the section Installing Heat Transfer Plateson page 25 for more information.

SuspendedThe next popular method of installingPEX UnderFloor is to suspend the tubing in the joist bay. Although this


PEX LockDown

Plywood Subfloor

RadiantPEX

Wood Screw, Minimum

118

"

138

"

34

"

12

"

12

"

5"

2'

3"

5"

6"

78

"

PEX Plates

1"2 Wood Screw, Minimum

Attachment Points

RadiantPEX

Aluminum PEX Plates.

Plastic LockDown fasteners.


method addresses several items raised by the plate method, it too hassome limitations.

A suspended installation does just that; it suspends the PEX in the joistcavity every 24"–32" with the use of aplastic clip or fastener. Watts RadiantLockDown fasteners eliminate noisefrom an underfloor application byallowing the PEX to quietly movewhile the PEX expands and contracts.

However, the cost of having a quietsystem is a reduction in heat transfer.Since the tubing is not in contact withthe subfloor, either directly or indirect-ly through heat transfer plates, theoverall BTU capacity of the system isreduced. For most suspended sys-tems the maximum BTU capacity ofthe floor is reduced to a maximumof 25 BTU/sq.ft.

Getting Started

Tools and MaterialsRequiredMake sure all materials are presentand in good working order beforebeginning a radiant installation. Thefollowing is a list of the most commonitems needed for a typical RadiantPEXUnderFloor radiant installation.

1. RadiantWorks reports. These reports help ensure the proper amount of tubing is installedin each area, along with the correctmanifold.

2. RadiantPEX tubing and corre-sponding number of fittings.There are two types of connectionsthat can be used with RadiantPEX:CrimpRing (installed with theCrimpAll Tool), and Compression(installed with a standard crescentwrench). Each fitting type isdesigned for ease of installation,durability, and longevity. Fittingsare typically chosen based oninstaller preference, unless other-wise specified.

3. Manifolds.Use only Watts Radiant mani-folds or Watts Radiant manifold components for field-constructed manifolds.

4. Unwinder.A required component for easily unrolling each RadiantPEX coilwithout kinks and twists.

5. Field repair kit. Each kit contains two barb-by-barbsplices and four RadiantPEX fittings.

6. Manifold mounting bracket.Brackets are used to temporarily orpermanently mount each manifoldpair to the floor or wall.

7. Watts Radiant heat transferplates and/or LockDowns andscrews or nails.

8. Pressure test kit.Each manifold pair must be pres-sure tested. This helps ensure eachRadiantPEX connection has beeninstalled correctly and to make sureno damage has been done to thetubing during installation.

9. Chalk line

10. Angle drill with 1-3/4" holesaw bit.

11. T-Square and marker.

Installation Steps:

Installation procedures will changefrom job to job and are affected byhow the structure is built. Joist spac-ing, bracing and zoning details are justa few items that can affect how an

Supply Manifold

Return Manifold

Exterior Wall

Exterior Wall

Typical RadiantPEX banding at exterior walls.



UnderFloor application is installed.The following guidelines and examples cover the most commoninstallation conditions. If unexpectedcircumstances arise, please contactWatts Radiant or a Watts RadiantRepresentative for assistance.

The most common installation patternin an UnderFloor application is a single serpentine layout.

Step 1: Install ManifoldsWith the use of Watts RadiantManifold Brackets or Manifold Box,secure the manifolds to the joist or wall enclosure. If the manifolds are located in the wall above the radi-ant floor, drill holes to transferRadiantPEX through the subfloor andinto the joist cavity below. If the mani-folds are located in the joist bay, simply attach the manifold enclosurehorizontally to the joist. Follow localcode guidelines when penetrating anyframing members.

Always keep the manifolds easilyaccessible.

Metal Manifold Enclosure located in wall.

Wall Stud

JoistBand Joist

RadiantPEX routed fromUnderFloor to manifold in wall.

RadiantPEX

RadiantPEX routed through joist in UnderFloor application. BOCA 2305.3.2 Guideline for joist penetration.


D

2" Minimum

Max. Bore Size:1/3 Joist Depth

Center Line

Penetration Zone

Joist Depth

1/3 D Max.

D

2" Minimum

2" Minimum

Step 2: Determine ZoneBoundariesBefore RadiantPEX is installed, visu-ally inspect the area to determine thezone boundaries. This helps determinewhere the first circuit is to be placed,while identifying any obstacles thatmay be in the way.

Step 3: Confirm TubingRequirementsMeasure the distance from the mani-folds to the farthest point in the zone.Make sure the RadiantPEX circuits aremore than twice this distance. If not,the RadiantPEX will not be longenough to reach the farthest point andstill have enough length to return tothe manifold.

Step 4: Drill JoistFor this step, gather the followingtools:

Chalk lineMarkerT-square1-3/4" bitAngle drillSafety glassesLadder

Measure 8" from the outside wall andmark the bottom of the joist. Locatethe last joist in the run and mark it 8"


from the outside wall. Snap the chalkline to mark the joists in between.With the use of the T-Square measurea drilling point in the middle of thejoist. Any hole drilled into a joist must be located between the mid-lineand upper 1/3 of the joist. Mark thehole location on each subsequent joist. This will help keep the holes in a straight line and make pulling theRadiantPEX much easier.

Step 5: Install the FastenersHeat Transfer Plate MethodHeat transfer plates are 24" long and5" wide. The size of the plates and the1/2" PEX limit the RadiantPEX spac-ing to 8" OC, or two runs per joist bay.

At each end of the joist bay make amark on the bottom of the subfloor3/4" from the joist (see figure (a) onthe next page). Snap a chalk line parallel to the joists between these two points. Repeat for the other joist.These lines will be used to line up theedge of the plate.

Secure the plate to the subfloor alongone side of the plate as shown. Theother side is to remain free to allowPEX to be installed and to minimizeexpansion noise associated with move-ment of the plates.

Position the plates approximately 12"away from the band joists or otherblocking to allow enough room for thePEX to bend. A maximum 6" spaceshould be left between plates. Thiswill help when inserting the PEX intothe plate later on.

In most cases it will not be possible toinstall plates evenly across the lengthof the joist bay. To figure out howmany plates will fit into the joist baytake the length of the bay and subtract2' from this length to account for thespace needed at either end. Take thenew length and divide this by 2.5 (thelength of one plate and the maximum6" space between plates). Round down


It may be necessary to loop the PEX before running through the joist to help absorb movement due tothermal expansion. Plates should be installed no farther than 6" apart. Space the plates so full plates are used. Do not attempt to cut the heat transfer plates to make them shorter as a rough edge may becreated that may damage the PEX tubing.

Schematics of PEX heat transfer plates.

5"

2'

3"

5"

6"

78

"

PEX Plates

1"2 Wood Screw, Minimum

Attachment Points

RadiantPEX


Although using LockDowns allow for tighter than 8" OC spacing of theRadiantPEX, it is still advised not to go much tighter. Closer spacingincreases the risk of kinking the bends.Standard bend radius for any size PEX piping should not exceed 8 timesthe nominal outside diameter.

LockDowns must be installed no farther apart than 32" and should support the PEX on both sides of abend. Ideal spacing is 24" OC.

At each end of the joist bay make amark on the bottom of the subfloor 3"away from the joist. Snap a chalk line parallel to the joists between these twopoints. Repeat for the other joists.These lines will be used to line up thescrews of the LockDown. Secure theLockDown every 24"–32" OC.

Position the first LockDowns approxi-mately 12" away from the band joistsor other blocking to allow enoughroom for the PEX to bend.


this number to the nearest whole number. This will give the number ofplates needed to fill the space in onejoist bay.

For example, in a room that measures20' long:

20' – 2' = 18'18'/2.5' = 7.2 plates

7 × 2 = 14 plates

14 plates are required for this bay.

The number of plates was doubled toaccount for both runs of tubinginstalled in this bay. The spacing ofthe last few plates may need to beadjusted slightly to allow the last plate to remain 12" off of the bandjoist or blocking.

Note: Do not cut the plates to make them shorter. This will poten-tially create a sharp or ragged edge that may cause damage to the RadiantPEX.

(a). Snap chalk line. (b). Install Plates. (c). Install PEX.

8"

34

"

6" 6"

8"

3"

7

1’ 1’ 34

"

34

"

34

"34

"

A bead of silicone should be added to the plate channel to help minimizenoise that may sometimes be gen-erated as the PEX tries to expand and contract.

Install enough plates to accommodatethe first circuit. Do not install platesacross the entire floor at one time as itmay become necessary to adjust platelocations as new circuits of PEX areinstalled. The next circuit of PEX willbegin 6"–8" off of the first circuit andthe next 6"–8" off of that one. It issometimes difficult to visualize whereeach circuit will end and the nextbegin. Correspondingly, it will be difficult to know where the next seriesof plates need to begin.

Suspension MethodSuspension systems are best installedwith Watts Radiant LockDowns. Thesame installation procedures should befollowed if other Watts Radiant attach-ment clips are used.


Install enough LockDowns to accom-modate the first circuit. Do not installLockDowns across the entire floor atone time. The next circuit of PEX willbegin 6"–8" off of the first circuit andthe next 6"–8" off of that one. It is difficult to visualize where each cir-cuit will end and the next begin.Correspondingly, it will be difficult to know where the next series of LockDowns will need to begin.

Step 6: Install the RadiantPEXPlace the unwinder underneath themanifold with a coil of RadiantPEXplaced over the center post. Place thesupport bracing down over theRadiantPEX and cut the binding tapeon the coil. Pull one end of theRadiantPEX off the unwinder and feed it through the guide eye on theunwinder. This will help prevent anykinking from taking place.

Before any PEX is pulled from theunwinder, first determine how manyjoist bays the first circuit will cover.

Take the required circuit length (foundon the RadiantWork’s Zone ListReport), subtract twice the distancefrom the manifold to the far joist bayand divide by twice the joist length.

First CircuitFor example, let’s assume we have aproject with 20' joist bays, is 30' × 20'in size and the design calls for 200'circuits. In this example the number ofjoist bays filled by the first circuitwould be calculated as follows:

200' – (2 × 30') = 140'

140'/(2 × 20') = 3.5 bays

Drill two series of holes in the joists to the far bay. The first one should be6"–8" from the band joist or joist support. The second should be 4"–8"away from the first.

Begin by pulling the PEX tubing down the second series of holes


3"1’

8"

2’

8"

712

"

Snap chalk line and install LockDowns. Install RadiantPEX.

LockDowns should be spaced no farther apart than 32". Where possible, LockDowns should be positioned around bends and turns to help support the tubing. Additional LockDowns may be used as necessary.


drilled, as shown. Create a hangingloop in the PEX that is 4'–6' long inthe third bay from the end. Createanother hanging loop in the next bayof the same length.

Do not pull the PEX straightthrough to the far joist bay.Depending on the ambient airtemperature at the time of installa-tion and the joist spacing, the PEX tubing may kink when tryingto pull a new loop.

In the last bay, pull enough PEX to fillthis bay and return to the manifold.When enough PEX has been pulled,return the PEX back down the otherseries of holes to the manifold.

Install the PEX in the far bay usingeither LockDowns or plates (theseshould already be installed before the PEX circuit is pulled).

If extra tubing is required, pull from the previous bay. Likewise, ifextra tubing is left over, push it back through the joist and into the previous bay.


Manifold location.

Pre-drill the joists to the far bay.Keep drill holes no closer than4" OC.

Determine which bays are toreceive RadiantPEX.

Return the PEX down theouter series of holes to themanifold.

Pull a 4'–6' loop in each bay.

Pull enough PEX to fill thefarthest bay.

Distance to farthest bay

Joistlength

5.3' is the equivalent of the first fourjoist bays the first circuit covered.Also, the 0.5 is the portion of joist baythat remained from the first circuit.

All new tubing should be pulled from the unwinder first and then fedthrough the bays, keeping the hangingloops 4'–6' in length.

For the next bay any extra PEX thatmay be needed to finish the joist baywill come from the loop of PEX hang-ing in the previous bay. It may be necessary to extend this loop beforepulling the second bay.

Continue this process until all threebays are filled. Cut the PEX from theunwinder and attach to the manifold.

Step 7: Repeat With Next CircuitRepeat the same procedure for this and all subsequent circuits. Manifoldconnection details can be found in the

Appendix of this manual. Be sure tofollow all appropriate steps and use allapproved fitting components and tools.

In some cases it may prove easier toleave the ends of the circuits unat-tached to the manifolds until all cir-cuits for the given zone are installed.In these cases, it is important to makesure both ends of a single circuit areselected at one time when making thefinal connections to the manifold. Onemethod to prevent cross circuiting theloops is to tape the corresponding endstogether with electrical tape when eachcircuit is installed.

Note: Do not use duct tape onRadiantPEX.

If the ends have not been taped, or ifthe tape did not hold, it is important toverify corresponding ends of the samecircuit are selected. To do this, chosetwo circuit ends and blow through one,with a thumb placed over the otherend. Air should be felt on the otherside, confirming both ends of the samecircuit have been selected. If air is notfelt, select another circuit end until airis detected.

Most coils of PEX will provide multi-ple circuits, depending on the design.In some cases scrap material may

Second CircuitThe second circuit will need to pick upthe remaining section of the last joistbay left by the first circuit.

To determine the number of completebays the second circuit will cover, usethe same formula discussed earlierwhen installing the first circuit.Subtract from this value the amount offree joist bay left by the first circuit.

Remember in our example the distanceto the farthest point is four joist baysless than the first circuit.

Our second circuit equation is figuredas shown:

200' – [2 × (30' – 5.3')] = 150.60'

150.60'/(2 × 20') = 3.76 bays

3.76 bays – 0.5 bays = 3.26 bays

The next circuit will cover approxi-mately 3.26 “new” bays. The value of


UnderFloor ApplicationsManifold

RadiantPEX Barb

RadiantPEXFastener

RadiantPEX

Manifold

Pressure Test Kit

POWDER RM. FOYER

BATHROOMMASTER

MASTER BEDROOM

Zone 1Main Living Area

Zone 2Main Sleeping Area

Typical UnderFloor application.



RadiantPEX

Insulation

Always install verticalinsulation at exterior walls.

Foil-faced batt insulation

R-13 to R-19 insulation is typical, depending on applicationand construction conditions. More may be needed.

2"–4" Air Gap Aluminum Plate

event of extensive damage, a WattsRadiant Repair Kit may be required.More information on the repair kitsand repair methods can be found in the Appendix.

For detailed information on the propersteps to conducting a pressure test,refer to the Appendix of the installa-tion manual.

Insulation Details

Insulation is one of the most importantfactors that can affect how a systemoperates and performs. Different con-ditions call for different insulationrequirements. Insulation should be aminimum of 3-1/2", or R-13, foil-faced fiberglass batt when the radiantfloor is installed over a heated space,such as a basement. 5-1/2", or R-19,foil-faced batts (or thicker, dependingon the climate) should be used whenthe area below the radiant floor isunheated or exposed to the elements.

Caution: The exterior band joistsmust be insulated with the sametype of foil-faced insulation to prevent any excess heat loss directlyto the outside.

remain at the end of the coil. Scrapmaterial is any length of tubing notlong enough to be a complete circuit.

Make sure to use as much of each cir-cuit as possible. If the last circuit islonger than needed, try not to cut itshorter. Shorter circuits have a lowerpressure drop and will tend to cause animbalance in the fluid flow. Some tub-ing may be removed from this last cir-cuit as long as the remaining lengthremains within 10% of the existingcircuits. For example, if 200' lengthswere installed, the last circuit can becut to a length of 180' and still main-tain a balanced system. If more than10% is in excess, run the remainingtubing along an exposed wall or inother areas of the zone.

In the event excess tubing cannot beutilized, balancing control will need tobe installed on the manifolds.

Step 8: Visual Inspection andPressure TestingAfter all the circuits are installed, takea few minutes to walk each circuit andvisually inspect the tubing for possibledamage caused during installation. If damage is found, repair it using anapproved Watts Radiant method. In the

The design calculations used inRadiantWorks are based on foil-facedinsulation. If a non-foil-faced insula-tion is used, the performance of theradiant system will be reduced by asmuch as 25%.

Foil-faced batt insulation is preferredbecause it completely seals the joistcavity, but a foil-faced, high tempera-ture board insulation, such as a poly-isocyanurate or extruded polystyrene,may be used. Make sure a properthickness board is selected to providethe required R-Value for the project.To ensure proper performance from aboard insulation, make sure the boardcreates a completely airtight cavity.Use foam sealants as needed to seal allair gaps.

The use of foil only or the use of afoil-faced bubble pack insulation isnot recommended by Watts Radiant.These products should only be used inconjunction with another type of insu-lation, such as a non-foil-faced batt ora blown-in insulation. Use of thesemethods should only be considered byprofessional installers who have hadprior successful experience with thesetypes of products and/or applications.

Special Joist ConstructionMore and more projects are using TJIjoists and open web trusses. Thesespecially engineered building joistsallow for greater loads and broaderspans. Although they may solve someof the construction issues, they doraise some challenges for a properradiant floor installation.

TJI JoistsTJI (Truss Joist International) flooringsystems are installed in a similar man-ner as conventional joists. The designof a TJI joist system is slightly differ-ent, consisting of a laminated corematerial that resembles an I-beam.Due to this design, the allowable spacebetween the two center supports isslightly wider than what would beseen in a conventional 16" OC joistsystem. A wider batt insulation isrequired to fill this space, typically a



19"-wide batt is required. The remain-ing installation details described earli-er should be followed.

Note: Heat is often lost from a joistbay through holes drilled for plumb-ing and electrical lines. To preventthis, install “foam spray” insulationin these holes.

Open Web TrussesCross bracing is applied to two mainheader beams to form a “W” style profile. This design allows for easyinstallation of radiant tubing and othercomponents such as electrical andplumbing. However, since a tight joistcavity is desirable, some previouslydiscussed guidelines need to be adjusted.

Air movement in a joist bay can be aproblem with radiant heat installations.Reduced radiant floor output is associ-ated with air movement from joist bayto joist bay or from joist bay to theoutside. In a conventional joist system,air movement is isolated to a singlebay. This is not the case with an openweb system.

To help seal the joist cavity, the insula-tion needs to be placed up against theheader plate of the truss. This will prevent air from moving from bay tobay and from moving downward to the environment below. By doing this,a 2" air gap is no longer a possibility. If the insulation is placed so it justextends into the header space, a1/2"–3/4" air space should be easilymaintained. It still remains critical that the insulation does not touch theradiant tubing.

Aluminum Plate

Suspension Clip

Typical TJI (Truss Joist International) cross-section.

Typical Web Joist cross section.

TJI Joist

Foil-faced batt insulation.

Insulation needs tomake contact withthe header beamto create a sealedcavity.

Open Web Trusses offer several advantages on large construction projects. Web Truss floors can carryheavier loads and can span greater distances.

Sandwich Application

Sandwich and SubRay® applicationsmimic UnderFloor in almost everyway except one. In a Sandwich appli-cation, the RadiantPEX tubing isplaced on top of the subfloor insteadof beneath. Four- to six-inch-widesleepers, 3/4" to 1-1/2" thick, areinstalled every 8" OC. Sleeper require-ments will vary depending on theattachment method used. These sleep-ers mimic the function of the joist inthe main floor, aiding support for theupper subfloor that will be added priorto the finished floor.

Sleepers should be installed perpendi-cular to the joists wherever possible.

In some cases, a sandwich applicationmay be installed over an existing slab.In these cases, the installation require-ments are the same as they are forSandwich applications over a framefloor. Variations occur in how the systems are insulated. Sandwich overslab applications must be insulatedbetween the sleeper runs to isolate theheat loss into the slab. This willrequire a thicker sleeper, typically a 2 × 4 will be used, giving a sleeperheight of 1.5".

Many contractors have discovered thebenefits of Watts Radiant’s SubRay®

flooring system. SubRay is a prefabri-cated sleeper and header system, pro-viding an easy, low profile installation.Further information on the SubRayinstallation techniques and require-ments can be found in the WattsRadiant SubRay Installation Manual.

Sandwich Installation Methods

Heat Transfer PlatesWatts Radiant offers an aluminumplate designed to be used with 1/2"Watts Radiant RadiantPEX.

The heat transfer plate is attached tothe sleeper and the RadiantPEX is theninserted into the plate. This allows thePEX to be separated from the subfloor,eliminating any potential noise issue.

However, this separation raises con-cerns relative to the conductive transfer of energy needed to deliverthe required heat to a space. The aluminum transfer plates offer thiscontact, allowing conduction to con-tinue from the RadiantPEX to theupper subfloor.

In most cases a PEX system installedwith heat transfer plates will still


Sandwich/SubRay application over frame floor.


Heat Transfer plates can be used to secure thePEX tubing to the sleepers. This method helps toincrease the system’s response time and helps toreduce tubing movement.


Floor Covering

Upper Subfloor

Subfloor

SubRay subfloor radiant system

RadiantPEX Pipe

Joist

Foil-facedInsulation

deliver the required BTU load to aspace. The maximum BTU deliveredwill typically be around 45 BTU/sq.ft.

It is important to install the aluminumplates in accordance to the specifiedinstallation details. Failure to do somay result in noise associated with thealuminum plates wanting to move dur-ing the heating process. Refer to thesection Installing Heat Transfer Platesfor more information.



Watts Radiant’s SubRay system is a fast and easy way to install PEX tubing above the floor. Refer to theSubRay installation manual for more details.

Watts Radiant’s LockDown fasteners can be used to secure the PEX tubing to the existing slab or subfloor. Insulation methods must be considered prior to the PEX installation.

Cross sections of the SubRay subfloor radiant system, over slab (left) and over frame floor (right).

ClipsAnother method of installing PEXin a sandwich application is to use a clip, such as Watts Radiant’sLockDown™. Although this method iseasier to install than heat transferplates, there are some design cautionsthat need to be followed.

LockDown installations keep the PEXfrom coming in contact with the uppersubfloor. This may cause a signifi-cant reduction in heat output from

the system, depending on the load,floor covering, etc. Secure the PEXon either side of a bend or corner. Onlong straight runs, the PEX should befastened every 24"–32". It is importantto secure the PEX often enough so it does not rise above the sleeper.

However, the cost of having a com-pletely quiet system is a reduction ofheat transfer. Since the tubing is nolonger in direct contact with the subfloor, either directly or indirectly

through heat transfer plates, the overallBTU capacity of the system isreduced.

SubRayThe fastest and easiest method forinstalling RadiantPEX above the floor is Watts Radiant’s SubRay sys-tem. SubRay is a premanufacturedsandwich system, complete with headers, sleepers and fasteners. It’s acomplete, ready-to-install system. Formore information on SubRay pleaserefer to the SubRay installation manual, a 24-page booklet packedwith installation guidelines and tips, or visit the Watts Radiant Web site,www.wattsradiant.com.

Getting Started

Tools and MaterialsRequiredMake sure all materials are presentand in good working order. Followingare the most common items needed:

1. RadiantWorks Reports. These reports help ensure the proper amount of tubing is installedin each area, along with the correctmanifold size.

2. RadiantPEX tubing and corre-sponding number of PEX fittings.There are two types of connectionsthat can be used with RadiantPEX:CrimpRing (installed with theCrimpAll Tool), and Compression(installed with a standard crescentwrench). Each fitting type isdesigned for ease of installation,durability and longevity. Fittingsare typically chosen based oninstaller preference, unless other-wise specified.

SubRay Sleeper

RadiantPEX Pipe

Subfloor

SubRay HeaderStick

3. ManifoldsOnly use Watts Radiant manifoldsor Watts Radiant manifold com-ponents for field-constructed manifolds.

4. Unwinder.A required component for easily unrolling each RadiantPEX coilwithout kinks and twists.

5. Field Repair Kit. Each kit contains two barb-by-barbsplices and four RadiantPEX corre-sponding fittings.

6. Manifold Mounting Bracket.Brackets are used to temporarily orpermanently mount each manifoldpair to the floor or wall.

7. Watts Radiant heat transferplates and/or LockDowns andcorresponding screws or nails.

8. Pressure test kit.Each manifold pair must be pressure tested. This helps ensureeach RadiantPEX connection hasbeen performed correctly and tomake sure no additional damagehas been done to the tubing duringinstallation.

9. Chalk line

Fasteners

It is important to chose a fastener typein conjunction with the floor construc-tion requirements. Different projectsmay have height limits imposed on thesystem. This limit may make a differ-ence in the fastener type chosen.

Caution: Make sure sleepers are cor-rectly chosen in accordance with theWatts Radiant fastener used. If thesleepers are too shallow, the fastenerwill become a high point, which maycause complications while installingthe upper subfloor or finished floorcovering.

Installation Steps

Installation procedures change fromjob to job and are affected by how thestructure is built. Sleeper spacing,thickness and zoning details are just afew items that can affect how aSandwich application is installed. Thefollowing guidelines and examplescover the most common installationconditions. If unexpected circum-stances arise, please contact WattsRadiant or a Watts RadiantRepresentative.

Step 1: Install ManifoldsWith the use of Watts Radiant’s mani-fold brackets or manifold mountingenclosure, secure the manifolds to thejoist or wall enclosure. If the mani-folds are located in a joist space, makeallowances for the PEX to transferthrough the wall base plate and intothe sleeper system. Follow local codeguidelines when penetrating framingbase (bottom) plates.

Step 2: Determine ZoneBoundariesBefore RadiantPEX is installed,visually inspect the area to deter-mine the zone boundaries. Thishelps determine where the first circuit is to be placed, while identi-fying any obstacles that may be inthe way.

Step 3: Confirm TubingRequirementsMeasure the distance from the mani-folds to the farthest point in thezone. The minimum RadiantPEXcircuit must be at least twice thisdistance. If not, the RadiantPEX willnot be long enough to reach the far-thest point and be able to return tothe manifold.



INCORRECT PEX CLIP INSTALLATION: Sleeper selection is too shallow for the clip height. To correctthis, a taller sleeper must be used, or a more shallow clip.

CORRECT PEX CLIP INSTALLATION: It is recommended to size the sleepers so that a slight gapresults between the top of the clip and the new subfloor or finished floor covering. Watts Radiant’sLockDown or SnapClip fasteners work great if you are using 2" x 4" sleepers.

Step 4: Sleeper Placement and SizingFor this step, gather the followingtools: chalk line, marker, circular saw,and sleepers. There are two main vari-ations to a Sandwich installation; eachis dependent on how the system willbe insulated. If the system is to beinsulated in the joist cavity, a WattsRadiant SubRay sleeper system shouldbe used. If the system is to be insulat-ed on top of the subfloor, between thesleepers, then the sleeper height needsto be chosen based on the insulationheight to still allow a 3/4"–1" verticalspace for the RadiantPEX and corre-sponding fastener. Most systems insulated on top of the subfloor need a 2" x 4" sleeper, or greater, with a1/2"–3/4" insulation board.

Place a position sleeper around thezone and all interior walls. This posi-tion sleeper will help keep theRadiantPEX away from exterior andinterior wall construction. This isimportant to help prevent damage tothe tubing that may be caused by wallfinishing or floor covering installation,such as carpet strips or other anchorpoints.

If insulating between the sleepers,sleepers are typically spaced 8" OC.This spacing is based on a standard3/4" subfloor being applied on top.

Whenever possible, run the sleepersperpendicular to the joist direction.This will help add stability and stiff-ness to the floor.

Step 5: Install the FastenersHeat Transfer PlatesHeat transfer plates are 24" long and5" wide. The size of the plates limitthe RadiantPEX spacing to 8" OC.

Note: If using SubRay, heat transferplates are neither necessary norrecommended. See the SubRayInstallation Manual or video formore details.

Install the sleepers across the room,maintaining a 1"–2" spacing betweenthem. This will result in a 1-1/2" section of the plate to be attached tothe sleeper.

In some cases it may be necessary toinstall a wider sleeper along the wallsthat run parallel with the sleepers,since 8" is not always evenly dividedinto a room’s width.

In most cases it will not be possible toinstall all the plates evenly across thesubfloor, keeping the 6" spacingbetween plates. To figure out howmany plates will fit along the sleepers,take the length of the sleeper and sub-tract 2' from this length to account forthe space needed at either end. Takethis new length and divide this by 2.5(the length of one plate and ideal 6"space between plates). Truncate thisnumber to the nearest whole number.This will give the number of platesneeded to fill the distance.

For example, a room is 20' long.

20' – 2' = 18'18'/2.5' = 7.2 plates

Seven plates are required for this sleeper run.

The spacing of the last few plates willneed to be adjusted slightly to allow the last plate to remain 12" away fromthe edge of the room.

Note: Do not cut the plates to makethem shorter. This will potentiallycreate a sharp or ragged edge thatmay cause damage to the PEX.



Secure heat transfer plates along one side to allow for thermal expansion. Do not over secure the plateas unwanted noise may occur.

PEX Fastener Min. SleeperSize Type Thickness

3/8" Plates N/ALockDown 1-1/8"

1/2" Plates 3/4"LockDown 1-1/2"

Add a bead of silicone to the plate tohelp minimize noise that may some-times be generated as the PEX tries toexpand and contract, as well asimprove heat transfer.

Install enough plates to accommodatethe first circuit. Do not install platesacross the entire floor at one time. Thenext circuit of PEX will begin 6"–8"off of the first circuit, and the next6"–8" off of that one. It is difficult tovisualize where each circuit will endand the next begin. Correspondingly, itwill be difficult to know where thenext series of plates need to begin.

LockDown FastenersSandwich systems can be installedusing a variety of attachment options.We recommend Watts Radiant’sLockDown fasteners, which fit thePEX loosely thereby allowing the PEXto expand or contract.

Although using LockDowns allow fortighter than 8" OC spacing of theRadiantPEX, it is still advised not togo much tighter. Closer spacingsincrease the risk of kinking and may

lines will be used to line up the screw of the LockDown. Secure theLockDowns every 24"–32" OC.

Position the first LockDown fastenerapproximately 12" away from the edgeof the wall to allow enough room forthe PEX to bend.

Step 6: Install the RadiantPEXPlace the unwinder beside the mani-fold with a coil of RadiantPEX placedover the center post. Place the supportbracing down over the RadiantPEXand cut the binding tape on the coil.Pull one end of the RadiantPEX offthe unwinder and feed it through theguide eye on the unwinder. This willhelp prevent any kinking from takingplace.

Pull the free end of RadiantPEX fromthe unwinder and begin placing italong the position sleeper to the farend of the room/zone, snapping theRadiantPEX into the LockDowns.Stop when the desired tubing lengthhas been reached. If possible, try toinstall full runs of tubing to minimizethe need to cut into a sleeper in mid-run. Secure the RadiantPEX back to the manifold and make thecorresponding connection onto thesecond manifold.


unnecessarily complicate the layout.Standard bend radius for any size PEXpiping should not exceed 8 times theoutside diameter.

LockDowns must be installed no far-ther apart than 32", and should supportthe PEX on both sides of a bend. Idealspacing is 24" OC.

At each end of the sleeper bay make a mark 3" off of the sleeper. Snap achalk line between these two points.Repeat for the other sleeper. These


Sleeper height needs to selected to allow for a slight gap between the clip used and the new floor covering. LockDowns are 1-3/8" tall and therefore work great with 2" x 4" sleepers.

Manifolds

Position Sleeper

SleeperRadiantPEX

Insulation

Joist

LockDown Fasteners

2" x 4" Sleepers

Subfloor


It is generally easier to install fullsleeper lengths and then cut transi-tion points in a sleeper run with a circular saw.

In most sandwich applications, clipspacing of 24" OC will be more thanadequate. However, depending on thesleeper depth, closer clip spacing maybe required. It is important to preventthe RadiantPEX from rising above thesleeper to prevent damage during theinstallation of the upper subfloor orfinished floor covering.

Note: If using SubRay, LockDownfasteners are neither necessary norrecommended. See the SubRayInstallation Manual or video formore details.

Additional fasteners may be requiredaround bends and corners to minimizestress on the bend, and to prevent thetubing from “curling” upward.

Step 7: Repeat With Next CircuitRepeat steps 4 through 6, keeping thenew series of sleepers spaced accord-ing to the required tube spacing. If apartial sleeper bay needs to be filled,cut in a new transition point 8" fromthe previous point for the new circuit.

Try to keep all circuits the samelength. If the last circuit is too long,try not to cut it. Shorter circuits have alower pressure drop and will tend tocause an imbalance in the fluid flow.Some tubing may be removed fromthis last circuit, or any previous cir-cuit, as long as the remaining length is within 10% of the existing circuits.For example, if 200' lengths wereinstalled, the last circuit can be cut to a length of 180' and still maintain abalanced system. If more than 10% isin excess, run the remaining tubingalong an exposed wall or in otherareas of the zone.

In the event excess tubing can not beutilized, balancing control will need tobe installed on the manifolds.

Step 8: Visual InspectionAfter all the circuits are installed, take a few minutes to walk each circuit and visually inspect the tubingfor possible damage caused duringinstallation. If damage is found, repairit using an approved Watts Radiantmethod. In the event of extensive damage, a Watts Radiant Repair Kitmay be required. More information onthe repair kits and repair methods canbe found in the Appendix.


Insulation Details

Foil-faced batt insulation is primarilyused when an air gap can be main-tained between the tubing and theinsulation. In the case of a Sandwichapplication, the air gap is to either side

of the tubing, not below the tubing. If the insulation is installed in the joistcavity, a standard Kraft faced insula-tion can be used. Make sure to installthe insulation tight against the subfloorto minimize any convective losses thatmay be generated. Note: This is achange from previous manuals.

The actual R-value of the insulationshould be the same as an UnderFloorapplication. The insulation should be aminimum of 3-1/2", or R-13, foil-faced fiberglass batt when the radiantfloor is installed over a heated space,such as a basement. 5-1/2", or R-19,foil-faced batts (or thicker, dependingon the climate) should be used whenthe area below the radiant floor isunheated or exposed to the elements.

If insulating above the subfloor, theninsulation between the sleepers shouldbe a foil-faced insulation board. Werecommend a high-temperature poly-isocyanurate board, such as Celotex®

Thermax®. Even though there is no airgap below the tubing, the foil will helpeven out the heat transfer across thesleeper spacing and the upper subfloor.

If using SubRay, an aluminized tapecan be used between the sleepers.

In the case of a Sandwich-over-Slabapplication, especially a basementremodel, an extruded polystyrene insulation board, such as Dow® BlueBoard®, is recommended. This is dueto the tendency for moisture to collectin basement areas, either because ofcondensation or high seasonal watertable levels. An extruded polystyreneboard will withstand moisture condi-tions better than a polyiscocyanurate.

Manifold

RadiantPEX Barb

RadiantPEXFastener

RadiantPEX

Manifold

Pressure Test Kit


Walls and Ceilings

Radiant floors have a limited amountof energy they can produce, usuallyaround 45–50 BTU/sq.ft. This limit isset by the maximum human comfortlimit of 85°F. Most of the time thislimit will be seen in areas such as sunrooms or vestibules. In cases likethese where auxiliary heat is some-times required, supplemental heat maybe added in the form of baseboard orfan coils.

Or, supplemental heat may be addedby simply increasing the radiant surface area.

Tubing can be installed in an interiorwall or ceiling to increase the radiantsurface area for a given room.

Walls and ceiling panels may also be used in cases where constructiondetails prohibit a radiant floor installation.

Installation requirements are the samefor both ceiling and walls as seen inother frame applications.

If Watts Radiant’s SubRay product isto be used for the ceilings or walls,consult the SubRay InstallationManual or video for further details.

Wall and Ceiling Applications


Insulation Board

Insulation Board

Plywood

NailerFoam Clip

LockDown

Nailer Wall Stud orCeiling Joist

Interior Wallor Ceiling

PlywoodBoard

Foil-Faced Batt Insulation

RadiantPEX transitioning from one joist/stud bay to the next

Interior Wallor Upper Floor

RadiantPEX(cross section)

With LockDown

LockDownFastener

Side View.

Top view of a wall application, or a side view of a ceiling application.


For most wall applications, it isadvised not to extend the systembeyond 4' above the floor. This is due to various penetrations associatedwith items such as pictures and shelv-ing. To minimize damage to the tubing, keep the installation below thelevel required for normal decoratingpractices.

Recessed WallOne method for installing a wall orceiling is to first install a drop panel.This drop panel will usually consist ofa 1" insulation board, but may also be1/4" or 1/2" plywood. Both will besupported by runners attached to thesides of the studs or rafters.

If a plywood drop board is used, insu-lation needs to be installed behind theplywood. Use LockDown fasteners,attached to the plywood, to hold thePEX in place.

If 1" or 2" insulation board is used,fasten ScrewClips to the insulationboard at 2' OC. Then attach the PEXto the ScrewClips.

SubRay 862In some cases, the wall or ceiling cavi-ty may not be deep enough to allowfor the RadiantPEX, insulation, andsupport material. In these cases, WattsRadiant SubRay 862 can be used. Thiswill go on top of the wall studs or ceiling joists.

A 2 × 4 support plate will need to beadded to either end of the wall to helpsecure the Header Stick. Make sure toselect the 15-mm SubRay product toaccommodate the 3/8" RadiantPEXtubing, and 18-mm SubRay productfor 1/2" RadiantPEX tubing.

SubRay Sleepers are installed acrossthe studs or joists with Grippersinstalled every stud (16" OC) to keepthe RadiantPEX in place.

Caution should be used when securingthe ceiling material, taking extra careto only nail into the studs or joists.

Stud

Nailer

Plywoodor

InsulationBacking

Plywoodor

InsulationBacking

4"8"

Supply/Return Manifolds


Stud

Typi

cal M

ax. 4

'


Refer to the SubRay 862 InstallationManual for more product and installa-tion information.

CautionsOne limitation to walls and ceilings isthe maximum allowable temperaturethe dry-wall can maintain. Accordingto the National Gypsum Company, themaximum operating temperature forwallboard and ceiling board is 125°F.Due to this limitation do not allowsupply fluid temperatures to exceed120°F. From a design perspective, donot allow the surface temperature toexceed 90°F.

If a different wall material is to beused, consult that product’s manufac-turer for specific temperature limits.

Wall Stud/Ceiling Joist

RadiantPEXSleeper


Header Stick

Header Stick

Gripper

16" OC


Support forHeader Stick

Corner Sweep

Gripper

(hinged open)

Slab-on-GradeApplications

Introduction Slab applications are one of the mostcommon applications used by com-mercial, as well as residential, radiantheating systems. The added thermalmass provided by a slab increases theoverall thermal efficiency of the sys-tem, while providing more even heatdistribution throughout the structure.

However, since the slab is in directcontact with the ground, energy can belost to the surroundings. To helpreduce these back and edge losses, cer-tain conditions must be met prior tothe radiant installation to help ensureproper system operation.

Site PreparationA radiant slab should be placed onwell drained base rock material. Sub-surface water will rob heat from aradiant slab faster than a boiler canproduce it. Basements and slabs

installed in hillsides should have gooddrainage to carry any subsurfacegroundwater away from the site. Theslab should be placed above an ampleamount of crushed rock or gravel.

Radiant slabs placed on low-lying,poorly drained soil or sand shouldhave at least 1" of extruded poly-


styrene (Dow® Blue Board®) insula-tion under the entire slab — even insouthern climates.

A radiant slab should never be placeddirectly on top of clay or organic sub-soil, as these materials can conductheat away from the radiant slab, andthe soils may shrink in volume whendirectly exposed to the heat of theslab. An intervening layer of four ormore inches of crushed rock or rivergravel should be installed above thesesoil materials.

Caution: A radiant slab shouldnever be placed directly on top ofsolid bedrock, as this material canrapidly conduct heat from the slab intothe earth. Crushed rock and/or insula-tion must be installed between the slaband rock.

Sometimes 1"–2" of sand is placed ontop of the coarser base rock material.This gives a smooth, level surface tolay down rigid insulation, and helpsprevent possible breakup of the rigidinsulation in high traffic areas prior toconcrete placement. The sand layeralso allows for more precise levelingto minimize any variation in the slabthickness.

Concrete Slab Applications

Insulated Slab on Grade.


Slab

RadiantPEX

Insulation

Rewire

Base

Insulation Details

Unlike a frame application where theinsulation is installed after the radianttubing, a slab application requires theinsulation to be installed first, makingthe insulation part of the structure.

In a slab on grade application there aretwo main areas to insulate: verticallyaround the perimeter of the slab andhorizontally underneath the slab. Bothwill aid in the slab’s response and efficiency. Of these two, the verticaledge insulation is the most importantbecause it prevents heat loss directlyto the outside environment. Horizontalinsulation helps decrease the slabsrequired start up time by isolating theheating mass from the ground massbelow. Typically, the system will see areduction of about 3–10% in overalloperational efficiency if a horizontalinsulation is not used, and as much as15–20% if vertical edge insulation isnot used.

Type of InsulationExtruded polystyrene insulation boardis recommended mainly because theinsulation board will be in direct contact with the soil. Extruded polystyrene insulation will not degrade

over time due to excess moisture orsoil acidity. “Beaded” insulationboards should not be used becausethey are not strong enough and willbreak down over time. This, in turn,will cause structural instability.

In most applications, 1" insulationboard is recommended. A thickerboard may be used if the slab is to beinstalled in a cold, aggressive climateand/or if heavier traffic loads dictatestronger (i.e., thicker) insulation.Always consult with an architect orstructural engineer to specify theappropriate insulation for the particu-lar application.

Foil-faced insulation is not required or recommended when insulating aradiant slab. Foil-faced insulation isused when an air gap is able to bemaintained. In the case of a slab appli-cation the tubing is completely encap-sulated in the concrete, eliminatingany air gap.

Watts Radiant does not recommendBubble-type insulation under a slabapplication until more research hasbeen done and performance hasbeen verified.

Special ConstructionConsiderations

Slab applications are generally the eas-iest to install. However, it is importantto remember what type of constructionsteps remain after the concrete slabhas been poured. In most projects, theconcrete is the first phase of the proj-ect. Interior walls and other supportsstructures still have to be installedwith most being mounted or secureddirectly to the slab. With this in mind,it is important to take some prelimi-nary steps to help protect the tubingduring construction.

Control JointsConcrete slabs will expand and con-tract due to thermal changes. To pre-vent damage to the slab, expansionjoints are used to control this move-ment. In some cases cut joints are usedto control where cracking is to occur.Make sure the tubing is protectedaccording to the requirements of thecontrol joint.

Design Parameters

For proper radiant design it is impor-tant to know the type of layers used inthe floor construction. As these layersincrease or change, variances in theheating system are required. Concreteis a very conductive material, allowingfor a wider spread in heat transferthroughout the mass. However, certainlimitations should be present to ensurecertain comfort levels are maintained.

RadiantPEX SpacingMost residential slabs use 12" tubespacing with some perimeter banding.In a few cases, where control oversupply fluid temperature is needed, anentire room may be installed at 6" OC.This may be the case in a high heatloss sunroom or pool area. For certainindustrial or commercial projects thespacing may be greater.

RadiantPEX is generally installed oneither rewire/rebar for concrete slab



InsulationBoard

Subgrade

RadiantPEX

Concrete

Rewire/Rebar

applications, or to the subfloor for thinslab applications. Closer spacing maybe used in areas of high heat loss, suchas an exposed wall with a high per-centage of glass. 9" OC spacing issometimes preferred in bathrooms,kitchens and entries. Closer tube spac-ing, up to 6" OC, may also be used inareas that have a low thermal conduc-tivity, such as areas with thicker thannormal concrete or dense floor cover-ing such as a carpet and pad.

It is important to note that simply dou-bling the amount of tubing does notdouble the floor’s heating output. Thefloor's ability to deliver heat to a roomis based on the floor’s surface temper-ature. The amount of radiant tubingand fluid temperature controls this sur-face temperature. More tubing, or

tighter spacing may allow for the same surface temperature to bereached at a slightly lower supply fluid temperature.

Watts Radiant’s RadiantWorks designsoftware generates a specific nomo-graph for each room in the design.Nomographs convey several key fac-tors associated with a room, such astube spacing, floor surface tempera-ture, floor heating intensity, mean(average) supply water temperatureand back and edge loss values.Nomographs are essential to any radi-ant design. More information on howto read and use a Nomograph can befound in the Appendix.

Perimeter BandingSix- and nine-inch RadiantPEX spac-ing is sometimes used along outsideexposed perimeter walls in residentialapplications. These high-density spac-ing areas are called perimeter bandsand tubing is generally spaced at halfthe primary spacing. Banded areasrange in width from 2' to 8', with thewider bands generally used in front oftaller exposed walls with a high per-centage of glass. A good rule of thumbis to use a perimeter band width of50% to 75% of the height of the wall.

Tools and MaterialsRequired It is a good idea to have all materialspresent and in good working orderbefore beginning an installation. Thefollowing is a list of the most commonitems needed for a typical slab instal-lation.

1. RadiantWorks Reports.These reports help ensure the proper amount of tubing is installedin each area, along with the correctmanifold size.

2. RadiantPEX tubing and corre-sponding number of RadiantPEXfittings.There are two types of connectionsthat can be used with RadiantPEX:CrimpRing (installed with theCrimpAll Tool), and Compression(installed with a standard crescentwrench). Each fitting type isdesigned for ease of installation,durability and longevity. Fittingsare typically chosen based oninstaller preference, unless otherwise specified.

3. ManifoldOnly use Watts Radiant manifolds or manifold components for field-constructed manifolds.


RadiantPEX routed below expansion joint into subgrade.

Radiant Slab

Radiant Slab

Expansion Joint

RadiantPEX

Rewire / Rebar

Protective Sleeve(foam insulation or PVC conduit)

Subgrade / Gravel

Expansion JointRadiantPEX

Rewire / Rebar

Subgrade / Gravel

RadiantPEX sleeved at expansion joint with foam insulation or PVC conduit.

min. 6"

min. 2"

Caution: Do not exceedthe minimum bendradius of the tubing.

min. 2"

min. 6"


4. Unwinder.A required component for easily unrolling each precut RadiantPEX coil without kinks and twist.

5. Field Repair Kit.Each kit will contain two barb-by-barb splices and four corresponding RadiantPEX fittings.

6. Manifold Mounting Bracket.Each bracket can be used to temporarily or permanently mounteach manifold pair to the floor orwall. Use either Watts Radiantbrackets or SnapClips to hold manifolds.

7. Watts Radiant Fasteners.

8. Pressure Test Kit.Each manifold pair must be pressuretested. This helps ensure eachRadiantPEX connection has beeninstalled correctly and to make sureno additional damage has been doneto the tubing during installation.

9. Installation Accessoriesa. Spray Paint — for marking

out zones and subzones, as well as areas not to be heated.

b. Electrical Tape — for temporarily mounting the manifolds or taping ends of tubing together.

c. Cable Ties, ClipTies,ScrewClips, or other approvedfasteners.

Since rewire/rebar is commonly usedin concrete slabs for structural integ-rity, it is common practice to attachRadiantPEX to the rewire/rebar. Thisis commonly done with the use ofnylon cable ties or Watts RadiantClipTies and Clipper tool. Eachsecures the RadiantPEX to therewire/rebar to prevent movement ofthe tubing during the concrete pour.

In applications where rewire/rebar isnot used and an insulation board isplaced underneath the slab, Watts

Radiant’s FoamStaples or Foam Clipscan be used to securethe RadiantPEX tubing directly to theinsulation board.Standard RadiantPEXstaples can be used ifa thin slab is installedover a wood subfloor.

For any attachmentmethod, it is impor-tant to secure the tub-ing at least every12"–18" OC. Thiswill prevent theRadiantPEX fromshifting during theconcrete pour. (SeeWatts Radiant catalogor binder for moreinformation on fasteners and tools.)

Slab Profile andGeneral Details

In slab-on-grade applications, it isimportant to maintain at least 2"–3" ofconcrete covering above the tubing.More coverage may be necessarydepending on the structural require-ments of the slab. The 2"–3" coverageis to ensure structural stability withinthe slab, allow for cut joints or framewalls to be applied and to allowenough space to float the aggregate.Consult with the project manager orconcrete installer to make sure thisdepth is appropriate.

Complete encapsulation of the tubingis required to prevent stress pointsfrom forming on the slab, which mayaccelerate cracking over time.

Installation Steps

Manifold locations, final concretethickness and zoning details are just afew items that are required for a successful radiant slab installation.The following guidelines and exam-

FoamBoard Stapler™

ClipTwister™ ToolSupply Manifold

Return Manifold

Exposed Wall

Banded Tubing

Inte

rior W

all

Primary Tubing

Typical slab tubing layout.




ples cover the most common installa-tion conditions. If your situation is not covered here or if unexpected circumstances arise, please contactWatts Radiant or a Watts RadiantRepresentative.

The most common installation patternfor PEX slab applications is a singleserpentine layout, although in somecases a double serpentine or a spiralpattern may be used.

Step 1: Pre-Pour ConditionsVerify all subgrade conditions areproperly prepared, all insulation isinstalled according to design condi-tions and rewire or rebar is in place.With orange spray paint, locate allinterior walls and other obstacles thatmay need to be avoided, such as toiletareas, sewer drains, and any structuralsupports that may penetrate the slab.

Step 2: Install ManifoldsLocate where the manifolds are to beinstalled. Drive two pieces of rebarvertically into the ground at this loca-tion. With the use of cable ties or elec-trical tape, temporarily secure themanifolds to the rebar. Remember tokeep the manifolds high enough toallow for the thickness of the concrete,the interior wall base plate and otherstructural items that may need to beinstalled after the pour.

After the concrete is poured and justbefore the interior walls are installed,the rebar may be cut to free the mani-folds. The manifolds can then bemoved if necessary, to fit the actualwall construction. Make sure to leaveplenty of slack in all RadiantPEX circuits (2'–5' is recommended). AWatts Radiant manifold box can beused to secure the manifolds withinthe new wall. Watts RadiantLockDowns and StrapDowns can beused to organize RadiantPEX comingfrom the floor and into the wall.

Secure manifolds torebar or other support

Roll out the RadiantPEX andsecure to rewire or insulationas described. Various attach-ment methods can be usedwith RadiantPEX.

Lay RadiantPEX across slabarea, keeping tubing spacedto design conditions.

Secure RadiantPEX every18" OC to the rewire, rebaror to the insulation.


Typical slab installation. RadiantPEX is installed using a single serpentine pattern.

Vertical Edge insulation isrequired along all exposedsides of the slab.

Horizontal Insulation should beinstalled under the entire slabfor optimum performance. Forcommercial and some residen-tial applications, horizontal insu-lation can be limited to theexposed perimeter.



Step 4: Confirm TubingRequirementsMeasure the distance from the mani-folds to the farthest point in the zoneby right angles. Make sure the mini-mum circuit length is at least twice this distance. If not, the RadiantPEXwill not be long enough to reach thefarthest point of the zone and return.

Step 5: Install the RadiantPEXPlace the unwinder underneath themanifold with a coil of RadiantPEXplaced over the center post. Place thesupport bracing down over theRadiantPEX and cut the binding tapeon the coil. Pull one end of theRadiantPEX off the unwinder and feed it through the guide eye on theunwinder. This will help prevent anyunwanted kinking from taking place.

Pull the free end of RadiantPEX fromthe unwinder and lay it along theperimeter walls to the farthest point in

the zone, keeping the RadiantPEX6"–8" from the edge of the slab. Thiswill help protect the tubing from pos-sible penetrations later on when theinterior and exterior walls areinstalled. RadiantPEX can be rununderneath interior walls as long asthe RadiantPEX is deep enough in theslab to prevent nails in wall platesfrom damaging the circuits.

It is helpful to have a second personsecure the PEX to the rewire/rebar as the coil is being pulled. Stop whenthe desired tubing length has beenreached. Secure the RadiantPEX backto the manifold and make the corre-sponding connection onto the secondmanifold.

Transition sleeves should be used toprotect the PEX from concrete trowelsand other construction actions as ittransitions from the slab to the wall.

Unless the zone has only one loop orhas a very short exterior perimeter, donot heat more than half of the perime-ter with one circuit.

Step 6: Secure the RadiantPEX Slab applications usually require someform of fastener, depending on theconstruction details. Most slab applica-tions use rewire or rebar to addstrength or crack resistance to the slab.In this application, the RadiantPEXattaches directly to the rewire/rebar bythe use of cable ties or ClipTie clipsevery 12"–18". If the slab is pouredwithout the rewire/rebar, other fasten-ers can be used that will secure theRadiantPEX directly to the foam insu-lation beneath the slab.

Make sure all bends and corners aresecurely fastened to prevent the PEXfrom curling, creating an unwanted

Typical slab application. RadiantPEX tubing installed 12" OC in a single serpentine pattern.


high point in the circuit. Leave 2'–5'slack on each circuit in case the mani-fold position needs to be adjusted fromits temporary location.

If cable ties are used, make sure all“tails” of the cable ties are either cutoff or turned downward to prevent anyunwanted surface protrusions.

Caution: Metal wire ties mayincrease the risk of damage to thePEX and are not an approved Watts Radiant fastener type.

Step 7: Repeat With Next CircuitRepeat steps 4 through 6, keeping thenext circuit spaced according to thedesign.

Try to keep all circuits the samelength. If the last circuit is too long,try not to cut it. Shorter circuits have alower pressure drop and will tend tocause an imbalance in the fluid flow.Some tubing may be removed fromthis last circuit, or any previous cir-cuit, as long as the remaining length iswithin 10% of the existing circuits.For example, if 200' lengths wereinstalled, the last circuit can be cut to alength of 180' and still maintain a bal-anced system. If more than 10% is inexcess, run the remaining tubing alongan exposed wall or in other areas ofthe zone.


Step 8: Visual InspectionAnd Pressure TestingAfter all the circuits are installed, take a few minutes to walk each circuit and visually inspect the tubingfor possible damage caused duringinstallation. If damage is found, repairit using an approved Watts Radiantmethod. In the event of extensive damage, a Watts Radiant Repair Kitmay be required. More information onthe repair kits and repair methods canbe found in the Appendix.



Step 9: The Concrete PourTo help detect possible damage causedduring the concrete pour, keep the sys-tem under pressure. If damage is done,locate the area in question and removethe section of tubing from the con-crete. Clean off the damaged area andinstall a Watts Radiant splice fitting.Wrap the fitting with electrical tape toprotect it from the concrete. Bring thecircuit back up to pressure to ensure aproper fit on the splice.


Some minor pressure changes willoccur due to the increased internaltemperatures of the concrete as itbegins the curing process. Fluctuationsin air temperature may also cause aslight change in the test pressure. Inmost cases, a 10–15-lb. drop in pres-sure over a 24-hour period is notuncommon. For more information onpressure testing, see the Appendix.

Rewire/Rebar

RailwayCable Tie

ScrewClip

ClipTie

FoamBoard Staple

Insulation

Subgrade/Earth

Slab

Various tube fasteners for slab applications.


Manifold

RadiantPEX Barb

RadiantPEXFastener

RadiantPEX

Manifold

Pressure Test Kit


Thin-Slab and Slab-CapApplications

Some construction details call for athin slab, or a lightweight concrete, tobe applied above the subfloor. Theseapplications offer increased soundquality to a room and an increasedthermal mass to the radiant heatingsystem. In some cases, thin slabs areused to act as a fire-stop from floor to floor.

Most thin-slab applications areinstalled during the initial constructionof a building, due to the increasedstructural requirements to carry theadded weight.

Most lightweight concrete productswill increase the floor height by 1-1/2"and the floor load anywhere between12 to 18 lbs./sq.ft. This increase inload usually means a modification tothe joist system and/or other supportmodifications. It is important to verifya floor’s ability to withstand theseloads prior to installing a lightweightconcrete product.

Design Parameters

For proper radiant design it is impor-tant to know the type of layers used inthe floor construction. As these layersincrease or change, variances in theheating system result. Portland andgypsum-based concrete are very con-ductive materials, allowing for a widerspread in heat transfer throughout themass. However, certain limitationsshould be present to ensure certaincomfort levels are maintained.

RadiantPEX SpacingMost thin slabs will use 12" tube spac-ing with some perimeter banding. In afew cases, where control over supplyfluid temperature is needed, an entireroom may be installed 9" or 6" OC.This may be the case in a high heatloss sunroom or pool area.

In a thin slab over frame floor applica-tion, RadiantPEX is generally installeddirectly to the subfloor with the use ofstaples and/or NailTites. If the thinslab is to be installed over an existingslab, LockDowns, SnapClips, orRailways may be used to secure theRadiantPEX.

Closer spacing may be used in areas of high heat loss, such as an exposedwall with a high percentage of glass;9"-OC spacing is sometimes preferredin bathrooms, kitchens and entries.Closer tube spacing, up to 6" OC, mayalso be used in areas that have a lowthermal conductivity, such as areaswith dense floor coverings such as acarpet and pad.

It is important to note that simply doubling the amount of tubing doesnot double the floor’s heating output.The floor's ability to deliver heat to aroom is based on its surface tempera-ture. The radiant tubing controls thissurface temperature. More tubing, ortighter spacing, allows for the samesurface temperature to be reached at a slightly lower supply fluid temper-ature.

Watts Radiant’s RadiantWorks designsoftware generates a specific nomo-graph for each room in the design.Nomographs convey several key factors associated with a room, such as tube spacing, floor surface tempera-ture, floor heating intensity, mean(average) supply water temperatureand back and edge loss values.Nomographs are essential to any radiant design. More information onhow to read and use a Nomograph canbe found in the Appendix.


Floor Covering

1-1/2" Thin Slab (for 1/2" RadiantPEX)

Subfloor

RadiantPEX

Joist

Insulation

Typical thin slab construction detail.

Thin-Slab Applications


Perimeter BandingSix- or nine-inch RadiantPEX spacingis frequently used along outsideexposed perimeter walls. These high-density spacing areas are calledperimeter bands and tubing is general-ly spaced half the main spacing.Banded areas range in width from twoto eight feet, with the wider bandsgenerally used in front of tallerexposed walls with a high percentageof glass. A good rule of thumb is touse a perimeter band width of 50% to75% of the height of the wall, or half a standard wall height.

Tools and MaterialsRequiredIt is a good idea to make sure all mate-rials are present and in good workingorder before beginning a radiant instal-lation. The following is a list of themost common items needed for a typical Thin Slab installation.

1. RadiantWorks Reports.These reports will ensure the proper amount of tubing is installedin each area, along with the correctmanifold size.

2. RadiantPEX tubing and corre-sponding number of RadiantPEXfittings.There are two types of connectionsthat can be used with RadiantPEX:CrimpRing (installed with theCrimpAll Tool), and Compression(installed with a standard crescentwrench). Each fitting type isdesigned for ease of installation,durability and longevity. Fittingsare typically chosen based oninstaller preference, unless other-wise specified.

3. Manifolds.Only use manifolds provided byWatts Radiant or Watts Radiantmanifold components for field constructed manifolds.


5. Field Repair Kit.Each kit will contain two barb-by-barb splices and four corresponding RadiantPEX fittings.

6. Manifold Mounting Bracket.Each bracket can be used to tem-porarily or permanently mounteach manifold pair to the floor orwall. Use Watts Radiant Manifoldbrackets or SnapClips to hold manifolds.


8. Pressure Test Kit.Each manifold pair must be pressure tested. This helps ensure each RadiantPEX connection has been performed correctly and to make sure no additional damage has been done to the tubing during installation.

9. Installation Accessories.a. Spray Paint — for marking out

zones and subzones, as well as areas not to be heated.

b. Electrical Tape — for temporarily mounting the manifolds or taping ends of tubing together.

c. LockDowns, SnapClips,Railways, staples, or other approved fasteners.

FastenersAlthough the Watts Radiant staplegun is the most useful attachment tool, other fasteners are available forareas where the staple gun can notreach. Watts Radiant’s NailTites areused to secure RadiantPEX at turnsand bends and in areas inaccessible tothe staple gun. Both staples andNailTites need to be installed every12"–18" along each run of PEX.

In a few cases, where it is impracticalto insulate in the joist cavity, anextruded polystyrene insulation boardmay be installed on top of the sub-floor, or over an existing slab prior to


Return Manifold

Supply Manifold


the new thin slab pour. In these cases,fasteners such as Watts Radiant’sFoam ScrewClips and Foam Staplesmay be used to secure the tubingdirectly to the insulation board. Theproper insulation board must be specified by an architect or otherstructural professional.

To speed the installation of theRadiantPEX in a thin slab application,staple guns can be fitted with anextension arm. This arm allows theinstaller to move quickly through the attachment process. If FoamScrewClips are used, a Watts RadiantClipTwister tool will speed the instal-lation. The ClipTwister is a 3'-longdrill bit that attaches to a 3/8'' standardcordless drill. Put a ScrewClip in theend of the ClipTwister, push the clipinto the foam and screw it in place.

Watts Radiant Staple GunFor details on the proper use of theWatts Radiant pneumatic staple gun,see the corresponding section underthe Staple Up Application.

Installation Steps

Installation procedures change fromjob to job and are affected by how thestructure is built. Manifold locations,final thin slab thickness and zoningdetails are just a few items that canaffect how a Thin Slab application isinstalled. The following guidelines andexamples cover the most commoninstallation conditions. If a situation is not covered here or if unexpectedcircumstances arise, please contactWatts Radiant or a Watts RadiantRepresentative.

The most common installation patternto use in a Thin Slab application is asingle serpentine layout, although insome cases a double serpentine maybe used.

Step 1: Install ManifoldsLocate where the manifolds are to beplaced. With the use of Watts Radiant'smanifold brackets or manifold mount-ing enclosure, secure the manifolds tothe wall. Allowances may need to bemade to allow the RadiantPEX totransfer through the wall base plateand into the thin slab. Follow localcode guidelines when penetratingframing base plates.


Step 3: Confirm TubingRequirementsMeasure the distance from the mani-folds to the farthest point in the zone.Make sure the minimum circuit lengthis at least twice this distance. If not,the RadiantPEX will not be longenough to reach the farthest point andstill have enough length to return tothe manifold.

Step 4: Install the RadiantPEXPlace the unwinder underneath themanifold with a coil of RadiantPEXplaced over the center post. Place thesupport bracing down over theRadiantPEX and cut the binding tapeon the coil. Pull one end of theRadiantPEX off the unwinder and feed it through the guide eye on theunwinder. This will help prevent anykinking from taking place.

Pull the free end of RadiantPEX fromthe unwinder and lay it along theperimeter walls to the farthest point inthe zone, keeping the RadiantPEX6"–8" from the edge of the slab. This


ScrewClip

FoamBoard Staple

Staple

NailTite


will help protect the tubing from pos-sible penetrations later on when thefinal floor covering is installed.

It is helpful to have a second personsecure the PEX to the subfloor as thecoil is being pulled. Run the PEX backand forth in a serpentine pattern. Stopwhen the desired tubing length hasbeen reached. Secure the RadiantPEXback to the manifold and make thecorresponding connection onto thesecond manifold.

Transition sleeves may be used to pro-tect the PEX from concrete trowelsand other construction actions as ittransitions from the slab to the wall. Unless the zone has only one loop orhas a very short exterior perimeter, donot heat more than half of the perime-ter with one circuit.

In most applications, a single serpen-tine layout will be used. In a fewcases, a double serpentine layout maybe used. The performance of the sys-tem is nearly identical with either lay-out option; however, installation issuesand construction details may make onemethod easier to install.

Walls and Built-InsIn most thin slab applications, built-inssuch as cabinets, showers and wallsare already in place before the thinslab is poured. This also means these

items are in place before the radianttubing is installed.

Walls and other structural memberscan often create unique situations withtubing layouts. Most structural coderequirements restrict the amount ofmaterial that can be removed from awall member. Because of this, it isadvised to try to run the RadiantPEXtubing through doorways when everpossible.

Step 5: Secure theRadiantPEX Most thin-slab applications requiresome form of fastener, depending onthe construction details. When a thinslab is being installed over a subfloor,standard staples are used. To helpreduce installation time, the stapleguns may be fitted with an extensionarm. Make sure the staple gun is set to100 psi and does not come in contactwith the RadiantPEX.

Other applications may use a foaminstallation board below the thin slab.In these applications, FoamBoardStaples or ScrewClips can be used. For slab-cap applications, useRailways. Railways can be glued orimpact-nailed to the existing slab. In each case, secure the RadiantPEXto the floor every 18".

Step 6: Repeat With Next CircuitRepeat steps 4 through 6, keeping thenext circuit spaced according to thedesign. Most thin slabs use circuitspacing of 6", 9", or 12" OC. Don’t

Thin-Slab Application

Return Manifold

Supply Manifold

RadiantPEX secured using Watts Radiant Railway fastener. Railways accommodate 3/8", 1/2", or 5/8"Radiant PEX (1/2" RadiantPEX shown).

RadiantPEX secured using standard Watts Radiant staples.

Plywood, Foamboard, or existing slab.

Plywood


space the tubing wider than 12" OC aspossible thermal striping may occur.Likewise, spacings tighter than 6" OCis not advised due to possible struc-tural conflicts with the thin slab mate-rial. If tighter spacing is required, con-tact Watts Radiant for further advice.

Try to keep all circuits the samelength. If the last circuit is too long,try not to cut it. Shorter circuits have alower pressure drop and will tend tocause an imbalance in the fluid flow.Some tubing may be removed fromthis last circuit, or any previous cir-cuit, as long as the remaining length iswithin 10% of the existing circuits.For example, if 200' lengths wereinstalled, the last circuit can be cut to alength of 180' and still maintain a balanced system. If more than 10% is in excess, run the remaining tubingalong an exposed wall or in otherareas of the zone.


Step 7: Visual Inspectionand Pressure TestAfter all the circuits are installed, take a few minutes to walk each circuit and visually inspect the tubing

for possible damage caused duringinstallation. If damage is found, repairit using an approved Watts Radiantmethod. In the event of extensive damage, a Watts Radiant Repair Kitmay be required. More information onthe repair kits and repair methods canbe found in the Appendix.


Insulation Details

Foil-faced insulation is primarily usedwhen an air gap can be maintainedbetween the tubing and the insulatingmember. In the case of a thin-slabapplication, the tubing is completelyencapsulated in the lightweight con-crete, eliminating any need for an airgap. At this point, the main goal is toprevent heat migration downward. Ifthe system is insulated in the joist cavity, a standard paper-faced insula-tion can be used. Make sure to installthe insulation tight against the subfloorto minimize any convective losses thatmay be generated. The actual R-valueof the insulation should be the same aswhat was illustrated for a Staple-Upapplication. The insulation should be aminimum of 3-1/2", or R-13, fiber-glass batt when the radiant floor isinstalled over a heated space, such as abasement. 5-1/2", or R-19, batt (orthicker, depending on the climate)should be used when the area belowthe radiant floor is unheated orexposed to the elements.

For a thin-slab application over anexisting concrete slab, 1" extrudedpolystyrene insulation board is recom-mended to isolate the new pour fromthe existing. If a 1" board is unavail-able or if space does not allow for a 1" board, a thinner board can be used.It is not recommended to go below a1/2" insulation board. The proper insulation board must be specified by an architect or other structural professional.

Thin Slab with SleepersSleepers are sometimes installed within a thin-slab application to allowfor points of attachment for futurefloor coverings. The most commonapplication is with a hardwood floor.

Caution: The thin-slab surface must contact the upper wood flooror subfloor. Thin slabs can shrinkduring curing, creating an air gapwhich will restrict heat transfer andthe floor’s overall output capacity.

RadiantPEX tubing stapled down to the subfloorwith paper-faced batt insulation located below inthe joist cavity. Since no foil facing is used, theinsulation has to be installed against the subfloor.

Board insulation is used to isolate the thin slabfrom the subfloor below. ScrewClips or FoamBoardstaples are used to secure the PEX to the foaminsulation board. Additional insulation may beadded below, in the joist cavity, for an increased R-Value.

RadiantPEX tubing stapled down to the subfloorwith paper-faced batt insulation located below inthe joist cavity. Since no foil facing is used, theinsulation has to be installed against the subfloor.A lightweight concrete filler is used between thesleepers for added sound quality and increasedthermal mass.


Manifold

RadiantPEX Barb

RadiantPEXFastener

RadiantPEX

Manifold

Pressure Test Kit


Commercial applications require special design considerations and flexibility. This is especially truewhen designing and installing a radiant floor over a steel deck or precast concrete floor.

Steel Deck

Steel decks are usually seen in com-mercial buildings and other areas thatwill experience light to moderateloads. There are several different typesof steel decks, ranging from 2'' anglechannels to 6'' square channels. Thesechannels will play a part in determin-ing the RadiantPEX spacing.

When possible, install RadiantPEXperpendicular to the ribbing on thesteel deck. If using Railways, fastenthem parallel to the ribbing.

There is only one way a steel deckapplication can be insulated, that beingunder the steel deck. In this configura-tion, it is almost impossible to insulateunder a steel deck system with battinsulation, since the support memberstend to be farther apart than thetypical 16'' OC. A board insulation istypically used.

In most slabs, rewire or rebar will beused, giving the installer a way tosecure the RadiantPEX. In some appli-cations fiberglass mesh will be usedinstead of rewire/rebar. In this caseRailways can be used.

Precast Slabs

Precast slabs are similar to a steel deckapplication with the exception of themain support layer. The precast slab isdesigned, in most cases, to be the floorsupport of the level above and the fin-ished ceiling for the level below.Because of this, it is difficult to insu-late a precast slab system. Insulationoptions need to be discussed with theproject engineer or architect.

Likewise, rewire/rebar may or may not be used in the cap pour. Fastenertypes are chosen based on theapproved construction requirements.

Steel Deck ApplicationsRewire/Rebar

RailwayCable Tie ClipTie

Various tube fasteners for steel deck slab applications.

Concrete

Steel Deck

Board Insulation

Electrical ChaseRadiantPEX

Rewire/Rebar

Concrete Cap

Precast Concrete

Electrical Chase RadiantPEX

Typical Slab over Steel Deck application. Insulation board is usually installed below the steel deck,minimum 1" thick.

Typical Slab over Precast application. Insulation location and fasteners are variables depending on thestructural requirements of the total mass. Consult with the structural engineer before choosing an insu-lation or fastening method.

Caution: Maintain a minimum 2"concrete thickness above tubingunless otherwise specified by astructural profesional.


SnowmeltApplications

IntroductionRadiant snowmelt and ice-removalsystems for concrete, sand, and brickpavers are installed in the same man-ner as shown for a standard concreteslab. The main differences tend to bethe tubing size. Due to the increasedpumping requirements for the higherloads, a larger diameter tubing is needed to keep an acceptably lowpressure drop.

Although there are several similaritiesbetween a slab snowmelt project and abrick paver project, there are someimportant distinctions.

Brick PaverRadiantPEX can be installed underbrick pavers for the purpose of snowmelting. However, it is important toobserve several cautions. While WattsRadiant does not hold itself as expertin the art of brick paving, there areseveral precautions to observe.The thickness of the paving bricksmust be selected according to the man-

ufacturer’s printed cautions and loadlimitations. Bricks not thick enough tosupport the design load will crackand/or shift in service.

There are three installation methodsdescribed below. Once a determinationis made as to which method is pre-ferred, RadiantWorks should be usedto take into account the insulationvalue of the concrete (or alternate basematerial), sand, and bricks over theheating circuits. Base, sand, and brickmaterials retard the passage of heat,and must be compensated in thedesign of the snowmelting system..

There are three general types of instal-lations for RadiantPEX installed underbrick pavers:

1. Concrete.The easiest and most predictable substrate is concrete, where RadiantPEX is typically embedded in the slab, and the bricks are adhered to the top of the slab. Consult with experts in the field to ensure that the correct adhesives are used to secure the bricks to the concrete, and the slab will meet the load requirements of the expected traffic.

2. In the First Course ofBase Material.The RadiantPEX may be imbeddedin the first course of base material.A local engineer should determinethe type of base material chosen, thethickness of the base, and the degreeof compaction. The depth at whichthe RadiantPEX is buried should bedetermined in consultation with thelocal engineering firm. The firstcourse of base material is typicallycompacted base rock, mixed withfines to present a relatively impervi-ous surface.

3. In the Second Course of Base Material.To improve system response, theRadiantPEX may be placed on topof the first course of base material.The RadiantPEX is then coveredwith approximately two or moreinches of smaller base material. The depth at which the RadiantPEXis buried should be determinedin consultation with the local engineering firm.

RadiantPEX installed in a sand and brick paver application.


Rewire/Rebar

RadiantPEX

Brick PaverSupply/Return Manifold

Base Material

Sand/Crushed Stone Layer


After the secondary base course isinstalled, a 1/2" to 1" layer of sandbase is placed and leveled. Bricks areplaced on this secondary base courseand often vibrated, so sand fills all thejoints between the bricks. Sometimesadditional sand must be swept into thebrick joints, again depending on thelocal engineer and contractor recom-mendations. The stability of the brickpavers is very dependent on thesebrick joints being properly filled withsand, and upon the perimeter of thebrick surface being firmly held inplace. If the perimeter of the bricks isnot secured, the bricks will tend todrift apart.

If sand is not present in the jointswhen the bricks are installed over base material, unwanted movement ofthe bricks may be experienced, result-ing in an uneven finished surface.Refilling the brick joints with sand is atask that may have to be repeated sev-eral times, or until all the joints arecompletely filled. Contact the localbrick supplier and local contractor forprofessional advice in this matter.

General Site PreparationSnowmelt slabs should be placed onwell compacted material, consisting ofrock or sand. Load issues need to bediscussed with a structural engineer orthe project supervisor.

The snowmelt area needs to bedesigned with drainage in mind. Waterwill run off of the snowmelt area inthe same manner as rain. Externalareas, such as water drain ways, outside the snowmelt zone may beblocked by snow, ice or slush. Drainlocations and runoff profiles need to be designed with winter conditionsin mind. In some cases, extraRadiantPEX tubing may need to beinstalled around drain lines to preventwater from freezing.

A radiant slab should never beplaced directly on top of solidbedrock, as this material can rapidlyconduct heat from the slab into theearth. Crushed rock and/or insulationmust be installed between the slab androck.

Sometimes 1" to 2" of sand is placedon top of the coarser base rock material. This gives a smooth, levelsurface to lay down rigid insulation (ifnecessary), and helps prevent possiblebreakup of the rigid insulation in hightraffic areas prior to concrete place-ment. The sand layer also allows formore precise leveling to minimize anyvariation in the slab thickness.

Insulation DetailsUnlike interior slab applications wherethe insulation is recommended, snow-melt systems often do not require insu-lation. This is due to:

1. Loading.Snowmelt areas will experiencehigher weight loads than standardinterior heating applications. Heavyvehicular traffic, such tractor-trailers, may cause the insulation to compress. This compressionincreases the risk of cracking in a slab.


RadiantPEX installed in a slab-on-grade snowmelt application.

Rewire/Rebar

RadiantPEX

Concrete Slab


Base Material


2. Heat Transfer.Heat moves to cold. The coldestpoint of a snowmelt system is thesurface. Heat will naturally movemore towards the surface than to theground below.

This is not to say insulation cannot orshould not be used on a snowmelt system. Areas that need a fasterresponse or are more hazardous willbenefit from insulation. Stairs, handi-cap access ramps, and sidewalks are a few areas which may benefitfrom insulation.

If insulation is used, a non-foil-faced,high-density, extruded polystyrene(such as Dow® Blue Board®) is recommended.

The use of foil-faced insulation is notrequired nor recommended when insu-lating a snowmelt slab. Foil-facedinsulation is used when an air gap ismaintained between the tubing and theinsulating member. In the case of asnowmelt slab or brick paver applica-tion the tubing is completely encapsu-lated in the bedding material, eliminat-ing any air gap. In addition, concretewill tend to degrade exposed foil over time.

Caution: Watts Radiant does notrecommend the use of bubble-type insulation under a slab applicationuntil more research has been doneand performance has been verified.If needed or specified by a struc-tural professional, use only extrudedpolystyrene, such as Dow® BlueBoard® or equivalent. Density andthickness should be specified by aprofessional.

Control JointsConcrete slabs will expand and contract due to thermal changes. Toprevent damage to the slab, expansionjoints are used to control this movement. In some cases cut jointsare used to control and direct cracking.Make sure the tubing is protectedaccording to the requirements of thecontrol joint.

Design Parameters

For proper snowmelt design, it isimportant know the type and thicknessof each layer used. As these layersincrease or change, variances in thesnowmelting load may result. Concreteis a very conductive material, allow-ing for a wider spread in heat transferthroughout the mass. Brick pavers do not have the same conduction rate and will require specific design considerations. It is important all layers of a snowmelt system are modeled correctly with the use ofWatts Radiant’s RadiantWorks design software.

RadiantPEX SpacingMost snowmelt systems will use9"–12" tube spacing with some areas,such as steps or in front of door open-ings, installed 6" OC.

Tools and MaterialsRequiredIt is a good idea to have all materialspresent and in good working orderbefore beginning an installation. Thefollowing is a list of the most commonitems needed for a typical snowmeltinstallation.

1. RadiantWorks Reports.These reports help ensure the proper amount of tubing is installedin each area, along with the correctmanifold size.


RadiantPEX routed below expansion joint into subgrade.

Radiant Slab

Radiant Slab

Expansion Joint

RadiantPEX

Rewire / Rebar

Protective Sleeve(foam insulation or PVC conduit)

Subgrade / Gravel

Expansion JointRadiantPEX

Rewire / Rebar

Subgrade / Gravel

RadiantPEX sleeved at expansion joint with foam insulation or PVC conduit.

min. 6”

min. 2”

Caution: Do not exceedthe minimum bendradius of the tubing.

min. 2”

min. 6”

2. RadiantPEX tubing and corre-sponding number of RadiantPEXfittings.There are two types of connectionsthat can be used with RadiantPEX:CrimpRing (installed with theCrimpAll Tool), and Compression(installed with a standard crescentwrench). Each fitting type isdesigned for ease of installation,durability and longevity. Fittingsare typically chosen based oninstaller preference, unless other-wise specified.

3. Manifolds.Only use Watts Radiant manifolds or manifold components for field-constructed manifolds.


5. Field Repair Kit.Each kit will contain two barb-by-barb splices and four correspondingRadiantPEX fittings.

6. Manifold Mounting Bracket.Each bracket can be used to temporarily or permanently mount each manifold pair to the floor or wall. Use either Watts Radiant brackets or SnapClips to hold manifolds.


8. Pressure Test Kit.Each manifold pair must be pres-sure tested. This helps ensure each RadiantPEX connection has been performed correctly and to make sure no damage has been done to the tubing during installation.

9. Installation Accessoriesa. Electrical Tape — for

temporarily mounting the manifolds or taping ends of tubing together.

b. Cable Ties, ClipTies, Screw Clips or other approvedfasteners.

Since rewire/rebar is commonly used in concrete slabs for structuralintegrity, it is common practice to

attach RadiantPEX to the rewire/rebar.This is commonly done with the use of nylon cable ties or Watts RadiantClipTies and Clipper tool. Each will secure the RadiantPEX to therewire/rebar in such a way to preventmovement of the tubing during theconcrete pour.

In applications where rewire/rebar isnot used or an insulation board is



RadiantPEX ClipTie Rewire or RebarSlab

Subgrade / Compacted Earth

Typical Snowmelt Slab on Grade with ClipTies.

RadiantPEX

Rewire or Rebar

Slab


RailWay

Typical Snowmelt Slab on Grade with Railways.

RadiantPEX with Cable Ties

Brick Paver


Typical Snowmelt Brick Paver with Cable Ties.

Sand/Stone Dust


placed underneath the slab, some addi-tional attachment devices can be usedto secure the RadiantPEX. Railwayscan be attached to subgrade with theuse of ground stakes or talons. WattsRadiant’s Foam Staples or Foam Clipscan be used to secure the RadiantPEXtubing directly to the insulation board.

For any attachment method, it isimportant to secure the tubing every12" to 18" OC. This will prevent theRadiantPEX from shifting during theconcrete pour. (See Watts Radiant’s Product Catalog or Web site for moreinformation on fasteners and tools.)

Application Profilesand General Details

In slab-on-grade snowmelt applica-tions, it is important to maintain atleast 2"–3" of concrete covering abovethe tubing. More coverage may benecessary depending on the structuralrequirements of the slab. The 2"–3"coverage is to ensure structural stabili-ty within the slab, allow for cut joints,and to allow enough space to float theaggregate. Complete encapsulation ofthe tubing is important to preventstress points from forming on theslab, which may accelerate crackingover time. In brick paver applicationsit is important to maintain a minimum1"–2" layer of sand or stone dustbetween the top of the tubing and thebottom of the paver, depending on therecommendation of the engineeringfirm responsible for the installation.

Installation StepsManifold locations, final concrete or sand thickness and zoning detailsare just a few items that can affecthow a snowmelt application isinstalled. The following guidelines and examples cover the most commoninstallation conditions. If a given situation is not covered here or ifunexpected circumstances arise, please contact Watts Radiant or aWatts Radiant Representative.

The most common installation patternfor snowmelt applications is a single


Manifold EnclosureRadiantPEX

Slab

Rewire/Rebar

Manifolds


Manifolds installed below grade in vault.

serpentine layout, although in somecases a double serpentine may be used.

Step 1: Pre-Pour ConditionsVerify all subgrade conditions areproperly prepared, all insulation (ifnecessary) is installed according todesign conditions and rewire or rebaris in place. With orange spray paint,locate any obstacles that may need tobe avoided. These may include trenchdrains or other structural supports thatpenetrate the slab, such as hand rails.

Step 2: Install ManifoldsLocate where the manifolds are to beinstalled. In most snowmelt systems,the manifolds will be located in anenvironmentally resistant box, such asan irrigation system box, and placed inthe ground. Some applications mayallow the manifolds to be mounted ina structural wall, such as in the exteri-or wall of a garage. With eithermethod, it is important to support themanifolds in such a way so they arenot damaged during the concrete orpaver installation.

Drive two pieces of rebar verticallyinto the ground at the manifold loca-tion. With the use of cable ties or elec-trical tape, temporarily secure themanifolds to the rebar. This will helpprotect from jobsite activity. Manifoldsplaced on the ground can be subject tounwanted damage.

After the concrete is poured, the rebarmay be cut to free the manifolds. Themanifolds can then be moved if neces-sary, to fit the final enclosure area.Make sure to leave plenty of slack inall RadiantPEX circuits (2'–5' is rec-ommended). A Watts Radiant manifoldbox can be used to secure the mani-folds within a structural wall. WattsRadiant SnapClips, StrapDowns, andClipRails can be used to organizeRadiantPEX coming from the floorand into the protective enclosure.


Step 4: Confirm TubingRequirementsMeasure the distance from the mani-folds to the farthest point in the zoneby right angles. Make the minimumcircuit length is at least twice this distance. If not, the RadiantPEX will not be long enough to reach thefarthest point and still have enoughlength to return to the manifold.

Step 5: Install the RadiantPEXPlace the unwinder beside the mani-fold with a coil of RadiantPEX placedover the center post. Place the supportbracing down over the RadiantPEXand cut the binding tape on the coil.Pull one end of the RadiantPEX offthe unwinder and feed it through theguide eye on the unwinder. This will help prevent any kinking from taking place.

Pull the free end of RadiantPEX fromthe unwinder and lay it along theperimeter to the farthest point in thezone, keeping the RadiantPEX 6"–8"from the edge of the slab.



Secure manifolds torebar or other support

Roll out the RadiantPEX andsecure to rewire or insulationas described. Various attach-ment methods can be usedwith RadiantPEX.

Lay RadiantPEX across slabarea, keeping tubing spacedto design conditions.

Secure RadiantPEX every12" to 18" OC to the rewireor rebar.

Typical slab snowmelt installation. RadiantPEX is installed using a double serpentine pattern.


It is helpful to have a second personsecure the PEX to the rewire/rebar as the coil is being pulled. Stop whenthe desired tubing length has beenreached. Secure the RadiantPEX backto the manifold and make the corre-sponding connection onto the secondmanifold.

Transition sleeves should be used toprotect the PEX as it transitions out of the slab.

In most applications, a single serpen-tine layout will be used. In a fewcases, a double serpentine layout maybe used. The performance of the sys-tem is nearly identical with either lay-out option; however, installation issuesand construction details may make onemethod easier to install.

Step 6: Secure the RadiantPEX Slab applications usually require someform of fastener, depending on theconstruction details. Most slab applica-tions use rewire or rebar to addstrength or crack resistance to the slab.In this application, the RadiantPEXattaches directly to the rewire/rebar bythe use of cable ties or ClipTie clipsevery 12"–18".

Make sure all bends and corners aresecurely fastened to prevent the PEXfrom curling, creating an unwantedhigh point in the circuit. Leave 2'–5'slack on each circuit in case the mani-fold position needs to be adjusted fromits temporary location.

If cable ties are used, make sure all“tails” of the cable ties are either cutoff or turned downward to prevent anyunwanted surface protrusions.

Caution: Metal wire ties mayincrease the risk of damage to thePEX and are not an approved Watts Radiant fastener type.

Step 7: Repeat With Next CircuitRepeat steps 4 through 6, keeping thenext circuit spaced according to thedesign.

Try to keep all circuits the samelength. If the last circuit is too long,try not to cut it. Shorter circuits have alower pressure drop and will tend tocause an imbalance in the fluid flow.Some tubing may be removed fromthis last circuit, or any previous cir-cuit, as long as the remaining length iswithin 10% of the existing circuits.For example, if 200' lengths wereinstalled, the last circuit can be cut to alength of 180' and still maintain a bal-anced system. If more than 10% is inexcess, run the remaining tubing alongan exposed wall or in other areas ofthe zone.


Step 8: Visual Inspectionand Pressure TestAfter all the circuits are installed, take a few minutes to walk each circuit and visually inspect the tubingfor possible damage caused duringinstallation. If damage is found, repairit using an approved Watts Radiantmethod. In the event of extensive damage, a Watts Radiant Repair Kitmay be required. More information onthe repair kits and repair methods canbe found in the Appendix.

For detailed information on the proper steps to conducting a pressuretest, refer to the Appendix of theinstallation manual.

Step 9: The Concrete PourTo help detect possible damage causedduring the concrete pour, keep the sys-tem under pressure. If damage is done,locate the area in question and removethe section of tubing from the con-crete. Clean off the damaged area andinstall a Watts Radiant splice fitting.Wrap the fitting with electrical tapeand/or pipe insulation to protect itfrom the concrete. Bring the circuitback up to pressure to ensure a properfit on the splice.

Some minor pressure changes willoccur due to the increased internaltemperatures of the concrete as itbegins the curing process. Fluctuationsin air temperature may also cause aslight change in the test pressure. Inmost cases, a 10–15-lb. drop in pres-sure over a twenty four hour period isnot uncommon. For more informationon pressure testing, see the Appendix.


Manifold

RadiantPEXBarb

RadiantPEXFastener

RadiantPEX

Manifold

Pressure Test Kit

Miscellaneous

Although a snowmelt installation isvery similar to a standard slab installa-tion, there are a few additional areasthat need to be discussed. These beingsteps and glycol.

StepsSteps are generally viewed as difficultareas for a radiant installation. Thereare two important areas to keep inmind when installing steps in asnowmelt application: tread area, andriser area.

Tread area is where ice and snow willhave the greatest build up. The edge ofthe tread is where the least amount ofmelting will take place since it will bethe farthest from the tubing. It is alsothe area that can cause the most haz-ards. When selecting an installationtechnique, keep these factors in mind.

The finished covering may also influ-ence which installation method isused; for example a standard slab ver-sus a stone cap over the slab. In addi-tion, the riser height will be a factor indetermining how much tubing can beinstalled.

RadiantPEX can be installed eitherparallel or perpendicular to the steptreads. Each method offers advantagesand disadvantages.

RadiantPEX installed perpendicular to the treads will tend to limit theamount of heat delivered to the riser.This application may be used if theriser height is shallow or if the snowload is minimal.

Parallel installations may be somewhatmore complicated to install, but theyoffer the most melting potential. Thisapproach will more easily melt snowand ice that may build up along theouter step edge. However, it mayrequire additional rebar to support thetubing around bends as it moves fromstep to step. As with all applications, itis important not to exceed the mini-mum tube bend radius (8 times the ODof the pipe) for the PEX when transi-tioning from step to step.

In both applications it is important tokeep the RadiantPEX 2''–3'' away fromthe surface of the concrete.

In some cases it may be ideal to installa designated manifold for the steps.This allows for a dedicated vent/purgeassembly to be used for purging thetubing located in the steps.

GlycolAny hydronic system that is exposedto near or below freezing conditionsmust have propylene or ethylene glycol installed as the working fluid.Glycol can prevent the system fluidfrom freezing. The level of frost protection will depend on the glycolconcentration used.

Glycol BasicsGlycol is naturally corrosive. Buffersand inhibitors are added to offset this corrosive effect. In addition, glycol acts like an “oxygen grabber,”absorbing any free oxygen moleculesin the system. The more oxygen theglycol “grabs,” the more acidic it will become.



Preferred Method: RadiantPEX installed running parallel with the steps. An additional run of RadiantPEXmay be installed in the riser of the step to help increase melting along the outer edge.

RadiantPEX installed running perpendicular with the steps. This method of installing RadiantPEXunder steps should be done with a certain level of caution because the point where the riser andtread meet may not receive proper melting due to its distance from the RadiantPEX. Although thismethod is not preferred over the parallel method shown above, it may be necessary due to con-struction or design constraints.

Tread Area

Riser Area

Rewire

RadiantPEX


Systems should not be operated at levels below 30% glycol. Glycol levelsbelow 25% do not contain enough corrosion inhibitors and may cause the glycol to act as food, allowingmicrobes to grow. The microbes feed,grow, and die, allowing a black sludgematerial to form in the system. In con-centrations above 25%, propylene glycol prevents microbe growth. Trynot to exceed a mixture level greaterthan 70% as the fluid may become tooviscous (thick) to circulate.

As glycol in the system ages, theinhibitors and buffers added to the system begin to break down. Thisprocess slowly returns the system tothe natural pH level of the glycol. Ifnot properly maintained, glycol in thesystem can cause corrosion. Check aglycol system at least once a year toensure the glycol is still within itsoperating parameters.

Caution: Do not install automotiveantifreeze in hydronic heating orsnowmelting applications. Also, do not install non-inhibited propyleneglycol. Either of these will harm the mechanical components of the system.

Glycol Maintenance

A glycol system should be checked fortwo things: system pH and freeze pro-tection. The quickest way to check aglycol system’s pH is with litmuspaper. If the pH drops below 7, thenmore buffers must be added to a sys-tem or the system needs to be flushedand refilled. There are only a limitednumber of times buffers can be addedto a system before it must be flushedand replaced. Check with the glycolmanufacturer for further details. Someglycol manufacturers will require ahigher minimum pH to be maintained.

Freeze Protection

The second item that must be checkedin a glycol system is the actual level offreeze protection provided. WattsRadiant recommends a 50% glycolsolution. However, this does notalways equate to a 50% glycol solu-tion and 50% water. Different glycolproviders supply different concentra-tions of glycol and/or may mix a cer-tain amount of distilled water with theinhibitors. For example, a glycol thatis already pre-mixed to a 50% leveland then is diluted by the installer with50/50 water have a true 25% glycolconcentration.

The only way to accurately measureglycol in a system is to use a refrac-tometer. A refractometer uses a simpleproperty of a liquid to determine itsfreeze point. Liquid will refract, orbend light at a known angle. Thisangle is a direct correlation to itsfreeze point. A refractometer is adevice that measures this deflection.

A basic refractometer is a device thatlooks like a kaleidoscope. The userplaces a drop of fluid on a lens on oneend and then looks through the otherend. What is seen is a chart that showsthe freeze point.

This should be checked before andafter the glycol is installed. Check asample mixture, one cup glycol andone cup water. Test this solution withthe refractometer to see what the system freeze protection will be. Dothis each time the system is refilledwith new glycol. Also, check thefreeze protection when the system pH is checked just to make sure thesystem is operating within the desiredparameters.

Caution: The refractometer usedmust be calibrated for propyleneglycol. A refractometer calibratedfor automotive (ethylene) glycol willnot yield accurate results.


10

0

-10

-20

-30

-40

Typical Refractometer image as seenthrough the view finder. The terminus linebetween the shaded area and the lightarea represents the freeze level of the fluidin question. In this case, the fluid beingtested is freeze protected to –15°F.

Swedged manifold can befield coupled to form a single 7-branch manifold assembly.

For more information on the variousmanifold options see the Watts RadiantProduct Catalog, or visit our Web siteat www.wattsradiant.com.

Field-ConstructedManifoldsSome installers prefer to build theirown manifolds on the jobsite. Coppermanifolds can be made of any sizecopper water pipe tubing. Manifoldsfrom Watts Radiant are made of type L copper for standard use, and ifrequested, type K copper for under-ground external applications.

Caution: Use only Watts Radiant Parts.

Do not use fittings that are not supplied by Watts Radiant. Connec-tions made with barbs or fittings supplied by other companies arespecifically excluded from any WattsRadiant warranty coverage.

Watts Radiant has found many fasteners supplied by other companiescan cause long-term damage to thecover of the tubing, possibly leading toleaking and/or premature RadiantPEXfailure.

Refer to Watts Radiant’s warrantyfor more information.

There are three main ways to field-construct a manifold.

1. CustomCut Manifolds: Manifold “sticks” from the factory are designed to be used with anyRadiantPEX barb. Installers can purchase prefabricated CustomCutsor base branch manifolds and field-solder various combinations of barbs and mini ball valves as thejob demands.

Manifolds

Copper and BrassManifoldsManifolds are used to transition fromsupply/return piping to RadiantPEX.Manifolds are usually copper or brassbodies, with brass branches attached tothe sides.

Factory-Supplied ManifoldsA variety of pre-manufactured mani-fold options are available from WattsRadiant, each specifically designed tomeet or exceed any job specification.

Among the various options are:Stainless Steel (extruded stainless steel)

Stainless steel manifolds are constructed of tubular stainlesssteel and range from 2 to 12 circuits. Each pair comes withflow meters, circuit balancingvalves and mounted brackets.

Standard Tubular (copper and brass)Standard manifolds are customfabricated to each project’s specifications with any numberof circuits in diameters from 1" to 6".

CazzBrass (cast brass)CazzBrass manifolds are con-structed of cast brass and comein either 3 or 4 circuits and cou-ple directly to each other to formlarger manifold sets. CazzBrassmanifolds come with the follow-ing options: blank, flow metersor balancing valves.

CustomCut (copper tube)CustomCut manifolds are premade manifolds that comewith 12 or 16 barbs. CustomCutmanifolds are then cut in thefield to the specific circuit number needed for each zone.

Swedged (copper tube)Swedged manifolds are pre-mademanifolds with 3, 4, or 5 circuits.One end of a Swedged manifoldis flared so it can directly coupleto another Swedged manifold.For example, a 3- and a 4-branch

Appendix


Supply Manifold

Return Manifold

RadiantPEX Barb

End Cap or Plug

RadiantPEX Barb

Mini Ball Valve

Fluid Flow

Fluid Flow

Typical Copper or Tubular Brass Manifold Pair.


2. Swedged Manifolds: Pre-assembled manifold sectionsthat sweat together as needed.

3. 1" x 1" x 1/2" reduced T-fittings can be soldered together forming a complete manifold. RadiantPEXbarbs are then soldered into the 1/2" fittings.

For each of the assembly options, the smallest trunk size used must be at least 1".

Other methods exist to construct manifolds, such as T-Drill machines or even a standard drill press.

Supply Manifold

Return Manifold

Fluid Flow

Fluid Flow

Direct Piping Option. This option will require some balancing once the manifolds have been installed.

Reverse Return Option A. This option shows the supply and return piping installed in the same direction.

Reverse Return Option B. This option shows the supply and return piping installed in the opposite directions.

Appendix

Maximum flow rate for a manifold is determinedby the velocity of the fluid. Maximum designvelocity for manifolds should be between 4–6 ft/sec.

Manifold Trunk Sizing

Manifold Flow Manifold Max. GPM Trunk Size

12 1"20 1-1/4"32 1-1/2"60 2"


Manifold Set-UpThere are two ways fluid can flowthrough a manifold pair: Direct, andReverse Return. Both are dictated byhow the RadiantPEX is attached to the manifolds.

Direct is the easiest to install, and inmost cases, the easiest to follow. Thedown side to this method is balancing.A Direct set up will tend to requiremore post-fill balancing. This is due tothe simple fact that the last circuit onthe manifold will see a potentiallyhigher pressure drop than the first circuit. This higher pressure drop willequate to less flow and less heat delivery from that circuit. To fix thisproblem, it is important to have mini ball valves installed on one orboth manifolds.

Reverse Return is the preferredapproach. It eliminates almost all needfor post-fill balancing. For this set up,the first circuit on the supply manifoldwill be the last circuit off the returnmanifold. Each circuit “sees” the same

manifold length, creating an even pres-sure drop across each circuit.

Both set ups depend on the simple factthat each circuit is the same length,give or take 10%.

If a “Long Manifold” is installed, it is imperative to set the manifold up ina Reverse Return fashion. This isessential when the manifold spans thelength of the zone.

Supply and return manifolds areinstalled along the length of the zone,

perpendicular to the floor joists. Tomake RadiantPEX connections simpler, we recommend running athird copper line so the supply mani-fold is being supplied hot water at oneend of the manifold array. The returnmanifold should then be dischargingcooler water at the opposite end of the manifold array, as illustrated.

If each joist space is relatively long, itmay prove beneficial to run only onecircuit for each joist space. A morecommon installation is to use one cir-cuit to supply the heat to several joist

Appendix

Return Manifold

Supply Manifold

Capped End

Flow

Flow

FlowCapped End

Long manifolds are installed perpendicular to the floor joists. To ensure balanced flow through each circuit, a reverse return method is recommended. A reverse return manifold requires a third copper line to be installed. This extraline allows each circuit to “see” the same total manifold length, thus creating a balanced system. Remember, “first in, last out.”

Return Manifold

Supply Manifold

Capped End

Flow

Flow

FlowCapped End

Return Manifold


bays — drilling holes through thejoists as necessary. However, neveruse both approaches in the same zoneunless circuit balancing valves areinstalled to balance the flow.

In the long manifold approach, mani-folds may be installed in the joistspaces by drilling a sequence of threeholes in each joist. An alternativemethod is to attach the manifolds tothe bottom of the joists. In either case,always install the manifolds so that allRadiantPEX connections are easilyaccessible for future balancing, airpurging, or maintenance.

RadiantPEX Circuit Balancing ValvesIndividual circuits can be isolated orbalanced with the use of circuit valves.

Circuit balancing valves are used toisolate and/or balance the flow of fluidthrough an individual circuit. Theymay be installed on any or all of thecircuits on a manifold. If used for balancing purposes only, they are usually installed on the return mani-fold. If used for isolation purposes, thecircuit valves need to be on both thesupply and return manifold.

RadiantPEX FittingsRadiantPEX requires special mechani-cal fittings, designed for higher tem-perature and burst pressure ratings.Watts Radiant provides two fittingoptions:

1. CrimpRing: CrimpRing fittings are composed of a ribbed barb thatfits into the PEX tubing and a ductile copper ring that is placedover the barb and PEX. TheCrimpRing is compressed over thePEX, against the barb, with the useof a special crimp tool.

2. T-20 Compression: Compressionfittings are composed of three maincomponents: the barb, the compres-sion ring, and the compression collar. The barb fits into the PEXwhile the compression collar is usedto draw the compression ring downaround the PEX and barb assembly.Three O-rings located on the barbensure proper fit against the PEXand manifold.

The Crimp fitting is a permanent con-nection. The Compression fitting is aremovable fitting that should not beover tightened. Maximum torqueallowance for the Compression fittingis 20 in-lbs.

Cautionsa. Do not solder near, or overheat,

any RadiantPEX connections.Extreme temperatures associatedwith soldering may seriously damage the RadiantPEX and willvoid warranty.

b.All RadiantPEX and brass fittingsurfaces must be clean and drybefore making the connection.

c. Whenever possible, avoid makingconnections or splices in inaccessi-ble locations.

d.Repairing RadiantPEX that hasbeen in service requires specialattention, particularly when glycolhas been used. Any residualamounts of glycol or any othercoating inside the RadiantPEXtube must be removed. Use waterand a swab or pad to remove theresidue(s), then allow the tube todry prior to connection.

Appendix

RadiantPEX BarbMini Ball Valve

CrimpRing Fitting

T-20 Compression Fitting


Field RepairsHeat GunMost jobsite damage will consist ofover bending, or kinking, theRadiantPEX tubing. To repair a kinkedcircuit, use a heat gun set on low tem-perature. Hold the heat gun approxi-mately 6"–8" from the damaged area.Continuously move the heat gunand/or roll the PEX under the heatedair to prevent a hot spot from forming.The PEX should turn a milky whitecolor as it heats up. During thisprocess the PEX will begin to return toits original shape. Allow the PEX tocool for 15 minutes before returning itto service.

If the heat gun is held too close, orheld on one spot for too long, the PEXcan be damaged. Damage usuallyoccurs as a hole in the PEX pipe andthe damaged area will need to berepaired using a splice.

SpliceJobsite damage does occur from timeto time. To prevent the need to replacea complete circuit of RadiantPEX,Watts Radiant provides a repair kit.Each kit contains two barb-by-barbsplices and four correspondingRadiantPEX CrimpRings or Compres-sion fasteners.

WARNING:Use Field Repair Kits only for therepair of RadiantPEX damaged inthe field. Read complete instructionsbefore beginning repairs. Do notsplice together multiple lengths ofRadiantPEX to make a single lengthlonger than design. Refer to previ-ous chapters in this manual for rec-ommended circuit lengths.

Caution:Use of materials not supplied by WattsRadiant to make a splice or manifoldconnection may eventually result inleaks. Watts Radiant’s RadiantPEXand fittings are engineered to worktogether. Watts Radiant extends nowarranty — expressed or implied — to

any failure or damage of any kindresulting from use of materials notsupplied by Watts Radiant (seeRadiantPEX warranty for specifics).

1. Cut the RadiantPEX.Make a straight cut-off on bothpieces of RadiantPEX to be splicedtogether.

2. Select the Correct Brass Splice.Use only Watts Radiant brass splicesand corresponding fittings to repairRadiantPEX.

3. Choose the Correct Fitting.Make sure to use correctly sizedCrimpRing or Compression Fittingfor making RadiantPEX connec-tions.

4. Make the Connection.

CrimpRingSlide a CrimpRing onto each end ofthe PEX, about 2" down. Slide thecrimp barb into each end of the PEXand slide the CrimpRing back overboth the PEX and the barb. Make sure the CrimpRing is positioned inthe middle of the barb with about 1/8" PEX showing. Center theCrimpAll crimping tool over the

CrimpRing and squeeze. The tool willbottom out when the fitting is com-plete. Do not crimp the ring at anangle as damage to the PEX mayoccur.

Use a Go/No-Go gauge to determine ifthe fitting is acceptable. If not, removethe crimp with the use of a heat gun,cut off 3"–4" of PEX and reapply.

Appendix

CrimpRing Splice

T-20 Compression Splice

CrimpRing Fitting


T-20 CompressionSlide the compression collar over thePEX with the threads facing the end ofthe tubing. Next, slide the compressionring over the pipe, followed by theinsertion of the barb. It is important tomake sure the end of the PEX is cutsquare in order for a proper seal to be created between the PEX and theO-ring insert at the base of the barb.

Note: The compression ring is unidirectional and should be placed on the PEX with the directional line positioned towards the end of the PEX.

Seat the barb against the male threadadapter (this should already be sweatonto the manifold) and pull the com-pression collar down and thread thecollar onto the male adapter. The com-pression ring will automatically slideonto the PEX and will compress as thecollar is tightened.

Tighten the collar with a crescentwrench or torque wrench to 20 in-lbs.of torque, or until tight and then 1/4turn further.

Do not overtighten the fitting asdamage to the PEX or compressionring may occur.

Pressure Test

After the RadiantPEX and manifoldshave been installed, it is time to pres-sure test each zone. Individual test kitsmay be field constructed or a factorysupplied kit may be used. The follow-ing directions are specially directed tothe use of Watts Radiant test kits,although the general principles remainthe same for field-built units.

Attach the pressure test kit to the man-ifolds. Watts Radiant manifolds andtest kits with optional unions, can easily be hand tightened to hold up to 100 psi. Make certain the rubber O-ring is properly seated beforethreading the unions together.

One half of the Watts Radiant test kithas a Schraeder valve (air valve) onside A. The other half, side B, has apressure gauge. Fill the system (air orwater, but not both) through side A.When filling with water, leave thedrain on side B open (side with thepressure gauge) until water comes out.Close the valve and fill until the zoneis pressurized to between 50 psi and100 psi. Do not test over 100 psi, asthis will ruin the gauge on the test kit.

If the temperature is below freezing,use air to pressure test. If a fluid mustbe used, use a 50/50 water/glycol solu-tion. Failure to use glycol may resultin frozen circuits.

Manifold

Pressure Test Kit

Pressure Gauge

Union

DrainSchraeder Valve

Appendix

T-20 Compression Fitting

DirectionalLine

When making a buried slab repair,protect the final splice assembly with adouble wrap of PVC electrician’s tapeor plastic shrink wrap.


Do not use compression fittings asrepair joints inside a slab pour.


The cool night air will usually causeless than a 10-psi drop in pressure asthe water or air contracts from thecold. If there is more of a pressuredrop, or if there are other reasons tobelieve there is a leak, spray a soapysolution on all connections and inspectfor leaks. If there are still concernsabout leaks, increase the test pressureto 100 psi and inspect each of the circuits. A leak should be visible.

Typical Nomograph

Nomographs are generated byRadiantWorks as design aids for con-tractors and engineers for optimizingradiant floor heating designs. Eachnomograph is customized for a specific room or zone within a project.The following is a brief explanation ofhow to interpret a nomograph.

Note: The accompanying slab nomo-graph is customized and should notbe generalized to frame floors, otherfloor coverings, other RadiantPEXsizes or differing indoor air temper-atures.

On the upper left hand corner of thenomograph you will see the systemdesign parameters. In this case, thenomograph is for a slab with 1/4" tilewhere the desired indoor temperatureis 70°F, the outdoor temperature is 0°,the project is at an altitude of 2000'and 3/8" RadiantPEX is beinginstalled.

The left vertical axis displays the radiant floor heat output intensity, asexpressed in BTU/hr/sq.ft. of radiantfloor surface.

The right vertical axis displays theaverage floor surface temperature. Theactual floor surface temperature will

vary ±1°F relative to the measurementlocation; that being taken over a cir-cuit or between two circuits. In generala system will need to be designed sothe average floor surface temperatureis 85°F or below. Higher surface temperatures can be used if allowed by ASHRAE guidelines and the floorcovering manufacturer.

The top axis on the nomographreflects the total heat loss through theedges and underneath the radiant floor. As the radiant floor heat lossincreases, the mean water temperaturein the floor also increases. This heatloss is expressed as BTU/hr/sq.ft. ofradiant floor. It is calculated for eachproject by RadiantWorks based uponthe actual design parameters whichinclude floor insulation, floor coveringand overall system design.

Nomograph for Breakfast/Kitchen Area: Slab Application, 3/8" RadiantPEX.© Watts Radiant.

Required Heat Load Line

Tube Spacing

Room’s Actual Conditions

Rad

iant

Flo

or H

eat O

utpu

t Int

ensi

ty [B

TU/h

r/sq.

ft.]

50

45

40

35

30

25

20

15

10

5

0

90

88

85

83

80

77

74

71

67

63

58

Effe

ctiv

e Fl

oor S

urfa

ce T

empe

ratu

re [°

F]

60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220

Mean Water Temperature [°F]98

6oc 9oc 12oc 15oc 18oc

Total Floor R-Value: 0.6Indoor Design Temp: 68 [°F]Outdoor Design Temp: 0 [°F]

Maximum Allowable Floor Surface Temperature

EXAMPLE ONLY

Appendix


The bottom horizontal axis shows theaverage, or mean, water temperatureflowing through the radiant circuits.This is not the entering water tempera-ture. For example, if the enteringwater temperature is 108°F and theexiting temperature is 88°F then themean temperature is 98°F, the averageof the two.

The diagonal lines illustrate the designpossibilities if the spacing of theRadiantPEX tubing is adjusted.

Each diagonal line shows the heat output of a different RadiantPEX spacing, under the same design param-eters. Changes in the RadiantPEXspacing, supply water temperature, orthe R-value of the floor covering willmake a difference in the heat output ofthe radiant slab.

This nomograph shows five possibleRadiantPEX spacings, ranging from 6"to 18" OC. Spacings greater than 12"are usually limited to certain commer-cial and industrial applications wherefloor temperature variations betweencircuits is not a design consideration.

Read the Nomograph from left toright. A possible solution exists wher-ever the horizontal line associated withthe heating intensity intersects thediagonal line associated with a particu-lar RadiantPEX spacing, as long as therequired floor temperature is below themaximum floor temperature. If this isnot the case, and the required floortemperature is higher than the maxi-mum 85°F floor surface temperature,auxiliary heat will be required.

Next, find the required mean watertemperature necessary to heat thegiven conditions. Mark the point onthe nomograph where the horizontalheat intensity line intercepts with ahose spacing. From that point, movedirectly down to the bottom axis. Thisis the required mean temperature.

For our example, the kitchen slabneeds to radiate 17 BTU/hr/sq.ft. andwe chose a RadiantPEX spacing of

12" OC. The mean water temperaturewhere these two lines intersect isabout 92°F, or 102°F supply tempera-ture (based on a 20° temperaturedrop). If a 6"-OC tube spacing is used,a mean water temperature of 87°F isrequired, or 97°F supply temperature.

This tool should be used with care, asthe RadiantPEX spacing necessary tomeet the load still may not satisfy thecustomer. For example, an 18"-OCradiant circuit spacing in a home oroffice would likely generate customercomplaints about uneven floor surfacetemperatures. Also, care must also betaken not to exceed the warranty temperature limits of Watts Radiantproducts and the installed flooringproducts. Generally speaking, meanwater temperatures of 140°F andbelow should be used for slab heatingand mean water temperatures of 150°F and below should be used forframe heating applications.

Pressure Drop Charts

Watts Radiant’s pressure drop chartsare available for all sizes ofRadiantPEX, for plain water, ethyleneand propylene glycol. Informationregarding the heat required by the cir-cuit (Qs), pressure drop in the hose (ft-hd/ft), flow rate (GPM), and watervelocity (ft/sec) can all be calculatedfrom these charts. The charts are cata-loged by average water temperaturesrequired to heat a radiant zone, rang-ing from 100°–180°F. The followingpressure drop charts are for an averagewater temperature of 120°F.

ExampleThe following example will demon-strate the use of these charts.

Assume the total heat required for aradiant zone is 16,000 BTU/hr. Four,200' circuits of 3/8" RadiantPEX areused with an average water tempera-ture of 120°F.

The pressure drop for a circuit in thezone is calculated by following thesesteps.

1. Determine the heat required for eachcircuit in the zone.(16,000/4 = 4,000 BTU/hr/circuit)

2. Find this number on the QS axis (leftside of the chart).

3. Draw a horizontal line until it intersects the diagonal line for 3/8" RadiantPEX.

4. Drop a line vertically to read thepressure drop per foot of tubing (0.02 ft-hd/ft)

5. Find the total length of the tubing inthe circuit including the distance toand from the manifold. In this exam-ple the manifold is located in thezone (total length 200')

6. Find the total pressure drop by mul-tiplying the circuit length (in thiscase, 200') by the pressure drop perfoot of heat (in this case 0.02 ft-hd/ft)

Note: Follow steps 1–6 for other cir-cuits if the heat output and/or lengthsare different. The pump head is chosenaccording to the circuit having themaximum pressure drop. The pumpGPM is the summation of the GPM forall the circuits served by the pump.

There are many other uses for pressuredrop charts as well. Water velocity is shown on the chart by the shortdiagonal lines that intersect the longerdiagonal lines for each specific size oftubing. If the flow rate or the heatrequired is known, the water velocitycan be found by tracing horizontallyfrom either axis. In the above example, the water velocity is approxi-mately 1.25 ft/sec. It is a good generalpractice to maintain water velocitiesabove 1 ft./sec and below 5 ft/sec. For instance, 3/8" RadiantPEX in 200' lengths should be designed totransfer at least 3,000 BTU/hr, and

Appendix


5/8" RadiantPEX in 200' lengthsshould ordinarily be designed to transfer at least 9,000 BTU/hr.

Flow rate per circuit at 20°F ∆Tcan be found by continuing hori-zontally from the heat required (Qs)per circuit (on the left side of thechart) and reading the flow rate on the right side of the chart.

In the above example, the flow rate foreach circuit is approximately 0.40

GPM at a ∆T of 20°F. The total flow rate to deliver 16,000 BTU/hr is4 (circuits) x 0.40 = 1.60 GPM.

Note that if the flow rates are to bemanually calculated, the required sup-ply temperature can make a significantdifference in the resulting calculations.All three of the following charts arefor fluids at a temperature of 120°F.Systems with antifreeze solutions willexperience a greater change in fluidproperties as temperature conditions

change. Do not use the followingcharts if the required fluid temperatureis expected to change by more than20°F.

Because of the lower heat carryingcapability of glycol, a good rule ofthumb is to add an extra 10% to theflow rate.

WARNING: NEVER USE AUTO-MOTIVE ANTIFREEZE IN ANYHYDRONIC SYSTEM.

3/8"

Tub

ing1/2"

Tub

ing

5/8"

Tub

ing

3/4"

Tub

ing

1 ft/sec

2 ft/sec

3 ft/sec

7 ft/sec

1.5 ft/sec

5 ft/sec

1.25 ft/sec

4 ft/sec

6 ft/sec

1" T

ubing

0.0001 0.001 0.01 0.10.030.02

1.0

40,000

30,000

20,000

10,0009,0008,0007,0006,000

5,000

4,000

3,000

2,000

1,000900800700600500

5

4

3

2

10.90.80.70.6

0.5

0.4

0.3

0.2

0.10.090.080.070.060.05

PRESSURE DROP (Feet of Head Pressure Drop per Lineal Foot of Tubing)

Watts Radiant Pressure Drop Chart for RadiantPEXTMTM

FLO

W R

AT

E (

GP

M)

AT

20

FT

∆T

Qs

HE

AT

RE

QU

IRE

D (

BT

U/h

r) F

OR

AR

EA

SE

RV

ED

BY

ON

E C

IRC

UIT

109876

50,000

60,00070,00080,00090,000

100,000

Pure Water at 120°F

Notes: 1. The heat required is the energy the boiler must deliver for the calculated heat output of a circuit. If only the net heat output of the circuit is known, multiply by 1.1 to get Qs, assuming the back and edges are insulated or space below is heated.

2. If the ∆T is different from 20°F, the value of Qs must be multiplied by 20/∆T.3. Numbers from 1–7 in graph show the average water velocity in the hose (ft/sec).4. This chart is for pure water only. It cannot be used for other liquid mixes.

Typical pressure drop chart for water systems.

Appendix

3/8"

Tub

ing

1/2"

Tub

ing

5/8" Tub

ing

3/4"

Tub

ing

1 ft/sec

2 ft/sec

3 ft/sec

7 ft/sec

1.5 ft/sec

5 ft/sec4 ft/sec

6 ft/sec

1" T

ubin

g

0.0001 0.001 0.01 0.10.03 1.0

40,000

30,000

20,000

10,0009,0008,0007,0006,000

5,000

4,000

3,000

2,000

1,000900800700600

500

5

4

3

2

10.90.80.70.6

0.5

0.4

0.3

0.2

0.10.090.080.070.06

0.05



FLO

W R

AT

E (

GP

M)

AT

20

FT

∆T

Qs

HE

AT

RE

QU

IRE

D (

BT

U/h

r) F

OR

AR

EA

SE

RV

ED

BY

ON

E C

IRC

UIT 50,000

50% Propylene Glycol/50% Water at 120°F


2. If the ∆T is different from 20°F, the value of Qs must be multiplied by 20/∆T.3. Numbers from 1–7 in graph show the average water velocity in the hose (ft/sec).4. This chart is for 50% propylene glycol/50% water mixture only.5. Remember to correct the flow rate for the different heat carrying capacity of propylene glycol, as opposed to plain water.


Typical pressure drop chart for propylene glycol systems.

Appendix


0.0001 0.001 0.01 0.10.03 1.0

3/8"

Tub

ing

1/2"

Tub

ing

5/8"

Tub

ing

3/4"

Tub

ing

40,000

30,000

20,000

10,0009,0008,0007,0006,000

5,000

4,000

3,000

2,000

1,000900800700600

500

5

4

3

2

10.90.80.70.6

0.5

0.4

0.3

0.2

0.10.090.080.070.06

1 ft/sec

2 ft/sec

3 ft/sec

7 ft/sec

1.5 ft/sec

5 ft/sec

4 ft/sec

6 ft/sec

0.05

50,000

1" Tub

ing



FLO

W R

AT

E (

GP

M)

AT

20

FT

∆T

Qs

HE

AT

RE

QU

IRE

D (

BT

U/h

r) F

OR

AR

EA

SE

RV

ED

BY

ON

E C

IRC

UIT

50% Ethylene Glycol/50% Water at 120°F


2. If the ∆T is different from 20°F, the value of Qs must be multiplied by 20/∆T.3. Numbers from 1–7 in graph show the average water velocity in the hose (ft/sec).4. This chart is for 50% ethylene glycol/50% water mixture only.5. Remember to correct the flow rate for the different heat carrying capacity of ethylene glycol, as opposed to plain water.

Typical pressure drop chart for ethylene glycol systems.

Appendix


Fan CoilBaseboard

RadiantPEX No-Sweat™ Baseboard, Fan Coil, and Manifold ConnectionsWatts Radiant’s RadiantPEX tubingoffers a unique solution to a commonproblem associated with baseboardand fan coil systems. Running supplyand return lines to these units can be achallenge, especially in renovationprojects.

Different techniques are used to con-nect RadiantPEX to baseboard, fancoils, or manifolds. It is important toprevent RadiantPEX from exceedingits minimum allowable bend radius. If

this radius can not be maintained, acopper elbow should be hard piped tothe unit prior to the installation of theRadiantPEX barb fitting.

Connection Details1. Choose the correct RadiantPEX

size for the design flow rate (seebelow).

2. Choose the corresponding fitting (CrimpRing or T-20 Compression).

3. Solder the RadiantPEX barb, orRadiantPEX elbow, onto the base-board, fan coil unit, or manifold. If an elbow is required, install this prior to installing the barb.

4. Slide the corresponding fitting over the RadiantPEX and then theRadiantPEX over the entire barb.Refer to the corresponding sectionof this manual for instructions on how to properly connectRadiantPEX fittings.

Follow additional installation instructionsincluded with the RadiantPEX fittings.

RadiantPEXBarb

RadiantPEX Fitting

RadiantPEX

RadiantPEX

RadiantPEXElbow Fitting

RadiantPEX Fitting

RadiantPEX

BASEBOARD - BTU/ft (estimated maximum output)

3/4" 1" 1-1/4"160°F 520 560 610170°F 600 650 700180°F 680 730 790190°F 760 830 900

FAN COILS - BTU (estimated maximum output)

1 GPM 3 GPM 5 GPM160°F 6500 7100 7300170°F 7400 8000 8200180°F 8000 8600 8950190°F 8400 9000 9400

6"

6"

Appendix

Support RadiantPEX within 6" on either side of a bend withStrapDowns or SnapClips. Supports need to be placed every24"–32" when hanging RadiantPEX in a horizontal position.Use Mid-run Bend Supports where necessary to ensurestraight, non-stressed entry into the fitting.

Near Boiler Pipingand Controls

The following schematics are providedas a guide for common applications.Other schematics are available fromthe local Watts Radiant representative.

Primary/SecondaryGenerally, the best way to pipe ahydronic system is referred to asPrimary/Secondary.

Primary/Secondary piping allows forbetter flow and temperature controlover the various components. Eachlayout is broken down into two basicsections: The Primary loop, or boilerloop and the Secondary loop, or zoneloop.

The Primary loop provides boiler pro-tection. Boilers must be operatedabove their condensing point, unlessthey are condensing boilers. If a boileroperates in that condition, corrosionwill begin to affect the boiler and willeventually lead to premature failure ofthe boiler.

In addition to condensation, boilersmust operate at a maximum tempera-ture rise, typically 20°–40°F. The primary pump is sized to ensure bothof these conditions are maintained

independent of the load or pipingrequirements of the individual zones.

The Point of No PressureChangeThe point of no pressure change is acondition that has been discussed inpiping manuals for decades. The theory stems from how boiler pumpsrespond to pressure differentials.Circulators, in order to function properly, need to pump into the zone(load). This condition will always create a positive-to-positive rise acrossthe impeller. The placement of theexpansion tank will greatly affect howthe primary pump achieves this goal.

The expansion tank controls where thepressure change in the system occurs.Expansion tanks always see the samepressure at their point of connection to the system. Points on either side ofthe tank will either be higher or lowerdepending on the primary pump location. To prevent cavitation andmaximize longevity and efficiency, the primary pump must be positionedso it “pumps away” from the expan-sion tank.

There are several books solely dedicat-ed to this piping practice which offer avery detailed explanation. For thismanual, we will assume the followingconditions:

1. The air remover, expansion tank andautomatic fill assembly are locatedat roughly the same location.

2. The primary pump is positionedafter the expansion tank in a “pump-ing away” position.

3. The primary pipe size is sized basedon the boiler load and flow require-ments.

How to Size a CirculatorCirculators, or pumps, are sized basedon the required load and piping lossfor a given zone. The heat load dic-

Expansion Tank

FuseTron and RelayBox

Air Remover

Circulator

Isolation Flanges

3-way Mix Valve

PRV Valve (AutoFill)

Backflow Preventer

Control

Sensor

Pressure Gauge

Temperature Gauge

Ball Valve

Boiler Drain

Gravity Check Valve

Spring Check Valve

Zone Valve

Legend

Appendix



tates the required flow rate (GPM) forthe zone. This can be calculated byusing the following equation:

Pure Water

BTU = GPM × 500 × ∆T

50% Glycol – 50% Water

BTU = GPM × 455 × ∆T

For most heating systems using a 20°Ftemperature drop it can be assumed

1 GPM = 10,000 BTU/hr

So, a system requiring 100,000BTU/hr will need 10 GPM of flow.

The other performance factor in sizinga circulator is the head pressure. Headpressure is the friction loss associatedwith the water moving against theinside surface of the tubing or pipe.The circulator should be sized to overcome this loss, while moving the required volume of system fluid.

The zone head pressure is the pressuredrop seen through the RadiantPEX circuits in a given zone. It is calculatedusing the pressure drop charts and isadded to the pressure drop associatedwith the supply and return piping.

Because the RadiantPEX circuits arealways plumbed in parallel, the pres-sure drop for an individual circuit isthe same as the zone pressure drop.

Example:

Zone “A” calls for 20,000 BTU/hr to be delivered to a zone with 5 200' circuits of 3/8" RadiantPEX. The manifold is located 20' from themechanical room.

Step 1: Determine the zone flow rate.The flow rate for the zone is 20,000/10,000 = 2 GPM

Step 2:Determine the circuit flow rate.The flow rate through each circuit is 2 GPM/5 Circuits = 0.40 GPM per circuit.

Step 3:Determine the zone pressuredropUsing the pressure drop chart forwater, the pressure drop per foot oftubing is 0.02 ft-hd/ft tubing. Thisgives a zone pressure drop of 0.02 ×200 = 4.00 ft-hd.

Step 4:Determine the pressure drop of the supply/return lines.Assuming 3/4" supply lines areinstalled, with a flow rate of 2 GPM. 0.015 × 40 (supply and return distance) = 0.60 ft-hd.

Step 5:Determine complete pump spec.The required pump load is 2 GPM at(4.00 + 0.60) or 4.6 ft-hd.

The actual pump required for this zone is selected using the given manu-facturer’s guidelines. This is usuallydone with the use of a pump curvechart. The chart is set up showing thepumps capacity at various pressuredrops. Choose the pump that bestreflects the needs of the system.

For this example, pump #2 is the best choice.

This information is readily availableon a pump sizing chart. These chartsare created by the pump manufacturerfor each pump model and should beconsulted before selection of a pumpcan be made.

Expansion Tank SizingWater will expand as its temperatureincreases. Since a hydronic heatingsystem with an expansion tank is aclosed system, the internal fluid volume is fixed. A simple ratio of howthe volume, pressure and temperatureof the system interact can be modeledby using a simplified version of theideal gas law.

PV = T(Pressure × Volume = Temperature)

1

2

3

2

4

6

8

2 4 6 8 10

10

Flow Rate (GPM)

Hea

d Pr

essu

re (f

t-hd)

Typical pump sizing chart. Make sure zone circulators are sized to include supply and returnpiping in addition to the zone piping requirements.

Appendix

With a fixed system volume, if the ini-tial water temperature is 50° and it israised to 180°, the internal pressurewill increase, since the volume can notchange. By quadrupling the internaltemperature, the internal pressure willalso quadruple, changing it from aninitial 15 psi to 60 psi. This can damage system components and/orcause relief valves to discharge.

In order to keep the internal pressureroughly the same, the system volumehas to change. The question is by howmuch? What tank size would berequired if the temperature changedfrom 50° to 180° and the fluid volumewas 20 gallons (approximately 2400'of radiant tubing). Since we are dealing with an incompressible fluid,elevation will factor into the totalexpansion rate of the system. A step-by-step form can be found in this section, along with other useful chartsfor determining component volumes.

Step 1:Determine the initial volume of thesystem. To do this, calculate the volume of fluid in the tubing, supply-return piping, and all other mechanicalcomponents.

Step 2:Determine the static pressure of thesystem. The static pressure is the forceexerted on the system from the weightof the water above the mechanicalroom. The relative elevation change of the system will dictate how muchstatic pressure is in the system.

Step 3:Determine the fill pressure of the sys-tem. This is the static pressure plus afactor of safety. In our case, 3 psi ismore than enough to account forminor piping variations within a floor.

Step 4:Find the allowable volume increase,which is a percentage, in the system.This percentage will be determined by maximum pressure rating for thesystem, which is usually dictated bythe pressure relief valve.

Step 5:Find what the actual volume increasewill be for the fluid. This is done bymultiplying the initial volume by thecorresponding temperature factor. Thehigher the temperature, the moreexpansion the fluid will undergo.

Step 6:Find the expansion tank volume bydividing the actual volume increase bythe percentage.

There are several educational books onthe market that describe primary/sec-ondary piping arrangements.

For more detailed information, pleaseread these other publications. Thismanual is designed to give a basicunderstanding of primary/secondarypiping and to offer several pipingschematics as well as some correspon-ding electrical diagrams. WattsRadiant is not responsible for the performance or functionality of theseillustrative diagrams to any particularproject. Please consult a professionalmechanical contractor or a WattsRadiant representative for detailedadvice.

Expansion Tank Sizing form

Step 1: System Volume

Determine the amount of fluid in the radiant tubing, supply and return lines and near boiler piping (include boiler and other accessories).

Pipe Length × Volume/Foot* = Fluid Volume

Radiant PipingSupply/Return Piping

Boiler Volume(see boiler manual)

Total Volume (TV):

Total System Volume Includes:Boiler (see manufacturer’s specifications) Optional Buffer TankFancoils RadiatorsRadiant Supply/Return Lines Additional Hydronic Components

Tank Size =

Fill Pressure = (# floors * 3.87 + 7 psi) + 14.7 =

Expansion Volume (EV) = Total Volume (TV) × Expansion Factor*

EV =

AF = =

Tank Size = =

* Expansion Factor can be found on the following page.

Expansion Volume (EV)Acceptance Factor (AF)

(Relief Pressure +14.7) - Fill Pressure(Relief Pressure +14.7)

(EV)(AF)

Appendix



Mixing OptionsControlling the supply fluid tempera-ture to the zones is one of the morecritical features of the mechanical sys-tem design. There are several ways toachieve this goal, including 3-way mixvalves, 4-way mix valves, injectionpumps, and even standard ball valves.The most common means is to useeither a three way mix valve or aninjection pump.

Mix ValvesNon-electrical mix valves are designedto provide a fixed supply temperaturewhenever there is a call for heat.

This reduced temperature is achievedby allowing a controlled amount ofhigh temperature boiler water to mix

with the cooler return water from thezone. It is important to choose a mixvalve that has enough flow volume forthe zone design.

Mix valves are sized based on a Cvvalue. This value corresponds to thepressure drop generated by a certainamount of flow. If a valve is rated witha Cv of 5, then the valve can move 5 GPM of fluid at 1 psi drop (2.31' ofhead) through the valve.

If only one zone is being pumpedthrough a mix valve, make sure thezone flow requirement is below the Cvvalue of the pump. If multiple zones(pumps) are to be supplied by onevalve, then make sure the combinedflow of the zones does not exceed the

Cv value of the valve. See followingpages for sample piping schematics.

To determine the pressure dropthrough the mix valve at a given flowrate, use the following equation.

S.G. is the specific gravity of the fluid.For water this is 1, for glycol this is1.15. P is the pressure drop throughthe valve.

The total pressure drop for the zone isthe combination of the pressure dropfound through the zone, supply/returnpiping and the mix valve.

Most manufacturers will provide thisinformation in a graph similar to whatis seen for pump sizing. Consult thecorresponding mix valve manufacturerfor more sizing information.

System Volume Chart

105 . . . . . . . . . . . . . . . . .0.004110 . . . . . . . . . . . . . . . . . .0.005115 . . . . . . . . . . . . . . . . . .0.007120 . . . . . . . . . . . . . . . . .0.008125 . . . . . . . . . . . . . . . . .0.010130 . . . . . . . . . . . . . . . . .0.012135 . . . . . . . . . . . . . . . . .0.013140 . . . . . . . . . . . . . . . . .0.015145 . . . . . . . . . . . . . . . . .0.017150 . . . . . . . . . . . . . . . . .0.018155 . . . . . . . . . . . . . . . . .0.020160 . . . . . . . . . . . . . . . . .0.022165 . . . . . . . . . . . . . . . . .0.023170 . . . . . . . . . . . . . . . . .0.025175 . . . . . . . . . . . . . . . . .0.026180 . . . . . . . . . . . . . . . . .0.028185 . . . . . . . . . . . . . . . . .0.030190 . . . . . . . . . . . . . . . . .0.032195 . . . . . . . . . . . . . . . . .0.033200 . . . . . . . . . . . . . . . . .0.035205 . . . . . . . . . . . . . . . . .0.037210 . . . . . . . . . . . . . . . . .0.039

Expansion FactorsWater Glycol

System ExpansionTemperature Factor

105 . . . . . . . . . . . . . . . . .0.0048110 . . . . . . . . . . . . . . . . . .0.006115 . . . . . . . . . . . . . . . . .0.0084120 . . . . . . . . . . . . . . . . .0.0096125 . . . . . . . . . . . . . . . . . .0.012130 . . . . . . . . . . . . . . . . .0.0144135 . . . . . . . . . . . . . . . . .0.0156140 . . . . . . . . . . . . . . . . . .0.018145 . . . . . . . . . . . . . . . . .0.0204150 . . . . . . . . . . . . . . . . .0.0216155 . . . . . . . . . . . . . . . . . .0.024160 . . . . . . . . . . . . . . . . .0.0264165 . . . . . . . . . . . . . . . . .0.0276170 . . . . . . . . . . . . . . . . . .0.030175 . . . . . . . . . . . . . . . . .0.0312180 . . . . . . . . . . . . . . . . .0.0336185 . . . . . . . . . . . . . . . . . .0.036190 . . . . . . . . . . . . . . . . .0.0384195 . . . . . . . . . . . . . . . . .0.0396200 . . . . . . . . . . . . . . . . . .0.042205 . . . . . . . . . . . . . . . . .0.0444210 . . . . . . . . . . . . . . . . .0.0468

System ExpansionTemperature Factor

Tubing ID RadiantPEX Fluid Capacity Type M Copper Fluid Capacity

3/8" ID 0.53 gal/100 ft. 8.31 gal/1000 ft.1/2" ID 0.96 gal/100 ft. 13.2 gal/1000 ft.5/8" ID 1.4 gal/100 ft. 18.1 gal/1000 ft.3/4" ID 1.9 gal/100 ft. 27.0 gal/1000 ft.1" ID 3.1 gal/100 ft. 45.5 gal/1000 ft.

1-1/4" ID N/A 68.2 gal/1000 ft.1-1/2" ID N/A 95.4 gal/1000 ft.

GPMvalve Cv rating[ ] × S.G. = P

3-way Mix Valve

Temperature Gauge

Appendix

2

Injection Pump SizingInjection systems incorporate a seriesof sensors, some on the control pipingto measure fluid temperatures, whileother sensors are located outside tomeasure outside air temperature. With this information the injectioncontrol is able to calculate the actualheat load and required water tempera-ture at any given time.

Why is this important? Non-electricalmix valves are set to provide a fixedtemperature all the time. This tempera-ture is set to handle the heating loadon the coldest day of the year. Thistemperature is only reached for a smallpercentage of the time. For the rest of the heating season, a mix valve isproviding temperatures that will behigher than required for the heat loadat most times.

Reset systems are continuously optimizing the heating system by modulating the supply temperature.This helps reduce the possibility ofpotential thermal swings associatedwith mild fall and spring days.

Injection pumps are sized the sameway zone pumps are sized.

Pure Water:

BTU/hr = GPM × 500 × ∆T

50% Glycol - 50% Water:

BTU/hr = GPM × 455 × ∆T

As a rule, an injection pump will besized for a smaller flow rate than thecombined secondary zones.

Each zone is designed around a 20°F ∆T. This is done for comfort andresponse of the heating system. Theinjection pump, on the other hand, is only responsible for transferringBTUs. This can be done with a higher∆T value. As the ∆T increases, theresulting GPM rate will decrease whilestill providing the same BTU delivery.

For example, assume a zone supplytemperature of 120°F, a zone returntemperature of 100°F and a boiler sup-ply temperature of 180°F. The zoneflow rate is 10 GPM. What size doesthe injection pump need to be?

Zone Pumps

Injection Pump

Primary Pump/Boiler Loop

Zone Return LinesSwing Check ValveBalancing Valve

Supply From Boiler

ManualFill/PurgeAssembly

Return To Boiler

Appendix



The system load can be figured usingthe equation for water:

BTUs = 10 × 500 × 20 = 100,000

The required flow rate for the injectionpump can now be determined.

100,000 = GPM × 500 × (180 – 100)

GPM = 2.5

The ∆T is figured using the supplytemperature and return temperatureacross the injection loop. This is theboiler supply temperature minus thezone return temperature.

Note: In most cases the pressure drop across the injection loop will be minimal.

Appendix

Piping and Electrical Diagrams

One zone off boiler

The schematic shown illustrates a single-zone system, where a non-electric mixing valve is being used. Piping Schematic

Electrical Diagram

Appendix



Multiple zones off boiler

The schematic shown illustrates amulti-zone system, where twonon-electric mixing valves arebeing used.

Piping Schematic

Electrical Diagram

Appendix

Multi zones off boiler with injection pump mixing

The schematic shown illustrates a multi-zone system, where two zoned circulators are being supplied by an injection pump.

Tekmar 353 Injection Control

Piping Schematic

Electrical Diagram

Appendix



Notes


Notes


Notes

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Radiant Floor ApplicationsRadiantPEX UnderFloor™ with LockDowns™

SubRay™ over Frame FloorSubRay is installed on top of anew or existing frame floorwhere access under-neath is limited orcompletely inacces-sible. Hardwood floorcoverings can beinstalled directly on topof the SubRay sleeper, reduc-ing the already low profile even further.

Install either 15-mm SubRay for 3/8" RadiantPEX, or 18-mmSubRay for 1/2" RadiantPEX.

Always install insulation under the floor between the joists. Non-foil-faced insulation can be installed if the insulation is indirect contact with the subfloor (no air gap). If an air gap is to be present, install foil-faced insulation.

SubRay™ over SlabSubRay is installed on top of a new or existing slab floor.SubRay’s low profilereduces the increasedheight of the finishedfloor, allowing foreasier installation, andreduced constructionmodifications to existing itemssuch as doors and cabinets.Hardwood floor coverings can beinstalled directly on top of the SubRay sleeper,reducing the already low profile even further.

Install either 15-mm SubRay for 3/8" RadiantPEX or 18-mmSubRay for 1/2" RadiantPEX.

It is recommended to install an insulation layer on top of the exist-ing slab prior to the installation of SubRay. In cases where a lower profile is required, or in areas that are not conducive to an insulation board due to weight loads, a plywood layer may be used.

RadiantPEX UnderFloor with PlatesRadiantPEX UnderFloor using Watts Radiant plates is anotherpopular installationmethod. RadiantPEX issecured to the subfloorusing 5" × 24" alu-minum plates with amaximum 6" spacingbetween plates. The aluminumplates ensure conductive contact ismaintained with the subfloor.

Foil-faced fiberglass insulation is installed (foil facing up), leaving a 2"–4" air gap between the foil and the underside of the subfloor. Always insulate exterior band joists in this application to prevent external heat loss.

Thin Slab over Frame FloorStaple the RadiantPEX down to the wood subfloor. Install a minimum of 3/4" of concrete mix above thetop of the RadiantPEX;more may be requireddepending on structuralloading. Use one of thenew gypsum-based mixes, orfiber-reinforced concrete.

Always install insulation under the floorbetween the joists. Non-foil-faced insulation can beinstalled if the insulation is in direct contact with the subfloor (no air gap). If an air gap is to be present, install foil-faced insulation.

Installing RadiantPEX UnderFloor using Watts Radiant LockDownfasteners is a popular installation method. RadiantPEX is securedto the LockDown every 24" OC to the bottom of the subfloor.

Foil-faced fiberglass insulation is installed (foil side facing up),leaving a 2"–4" air gap between the foil and the underside of the subfloor. Always insulate exterior band joists in this application to prevent external heat loss.

Documents

MANIFOLDSmedia.wattswater.com/RadiantPEXManual.pdf · mum of 2" of portland concrete mix above the RadiantPEX; more may be required depending on structural loading. Use a foil-faced