The calorific value of a fuel is the quantity of heat produced by its combustion – at constant pressure and under conditions known as “normal ” of temperature and pressure (i.e. to 0oC and under a pressure of 1,013 mbar).

The combustion of a fuel product generates water vapor. The Higher Calorific Value supposes that the water of combustion is entirely condensed and that the heat contained in the water vapor is recovered.

The Lower Calorific Value supposes that the products of combustion contains the water vapor. The heat contained in the water vapor is not recovered.

When discussing the price of natural gas it is also important to know what price is quoted, i.e. the higher heating or the lower heating value