Calorific value

The energy present in a substance that is determined by heat produced by the combustion of that substance

Expressed in joules per kilogram

Gross calorific value Net calorific value

It is defined as a the quantity of heat cooled by the complete combustion of unit mass of the fuel in air or oxygen and the production of combustion are brought down to normal temperature

It is defined as the quantity of heat cooled by the complete combustion of a unit mass of the fuel and the products of combustion are let off into the atmosphere