The amount of heat produced by the complete combustion of a unit quantity of fuel. The gross of higher heating value is that which is obtained when all of the products of combustion are cooled to the temperature existing before combustion, the water vapor formed during combustion is condensed, and all the necessary corrections have been made. The net or lower heating value is obtained by subtracting the latent heat of vaporization of the water vapor, formed by the combustion of the hydrogen in the fuel, from the gross or higher heating value.