The heating value indicates the maximum usable heat volume that is produced during combustion of fuels such as fuel oil or LPG. The heat of the condensing water vapour cannot be used.
For the purpose of definition: In some cases the heating value and the calorific value of a fuel are not differentiated precisely, sometimes they are even treated as synonyms. This is wrong.
The heating value Hi – previously referred to as the lower heating value Hu – takes into account only the heat produced during the combustion, not the condensation heat produced in the exhaust gas. The heating value is usually only significant for older heaters, because they cannot use the energy of the condensation heat.
And this is the difference between the heating value and the calorific value. The calorific value Hs – previously referred to as the upper heating value Ho – indicates the thermal energy resulting from the combustion as well as the energy from the condensation heat. The efficient use of energy is carried out using modern gas or oil heating devices.
When comparing multiple fuels, it is irrelevant whether you compare them on the basis of the heating value or the calorific value, because: If the heating value of one fuel is higher than of another, the calorific value must also be higher – provided all other factors remain the same.
Fuel oil EL has a heating value of 10.00 kWh/l (kilowatt hours per litre) and a calorific value of 10.60 kWh/l.
Due to the same measurement unit, propane can be compared well with fuel oil. While propane has a heating value of 6.58 kWh/l in liquid state, the calorific value is 7.17 kWh/l. Given in kWh/m³ (kilowatt hours per cubic metre), the heating value and calorific value of the LPG are 25.80 and 28.10, respectively.
The heating value of natural gas E can be between 9.40 and 11.80 kWh/m³, the calorific value between 10.40 and 13.10 kWh/m³. Natural gas therefore has a lower energy value than propane and consequently also than fuel oil.
Note: All listed values are approximate. The actual values may differ depending on the region, temperature and composition.