Lower and Higher Heating Values of Gas, Liquid and Solid Fuels

The higher heating value (also known as gross calorific value or gross energy) of a fuel is defined as the amount of heat released by a specified quantity (initially at 25°C) once it is combusted and the products have returned to a temperature of 25°C, which takes into account the latent heat of vaporization of water in the combustion products.

https://courses.grainger.illinois.edu/npre470/sp2018/web/Lower_and_Higher_Heating_Values_of_Gas_Liquid_and_Solid_Fuels.pdf