The heating values for liquid fuels in units of Btu/lb are calculated based on heating values in unit of Btu/gal and the corresponding fuels density values. The higher heating value (also known gross calorific value or gross energy) of a fuel is defined as the amount of heat released by a specified quantity (initially at 25☌) once it is combusted and the products have returned to a temperature of 25☌, which takes into account the latent heat of vaporization of water in the combustion products.
The lower heating value (also known as net calorific value) of a fuel is defined as the amount of heat released by combusting a specified quantity (initially at 25☌) and returning the temperature of the combustion products to 150☌, which assumes the latent heat of vaporization of water in the reaction products is not recovered.
