Calorific value (HHV / LHV)
The heat released by complete combustion of a unit quantity of fuel; the higher (gross) value includes condensation heat of water vapour, the lower (net) value excludes it.
A fuel's calorific value or heating value can be stated in two ways:
- Higher heating value (HHV, gross calorific value): assumes combustion products are cooled to 25 °C and the water formed condenses, releasing its latent heat (about 2.44 MJ per kg of water)
- Lower heating value (LHV, net calorific value): assumes water leaves as vapour, so latent heat is not counted
LHV/HHV ratios: hydrogen 0.85 (120 / 141.8 MJ/kg); natural gas about 0.90 (50 / 55.5 MJ/kg methane); diesel/gasoline about 0.93–0.94; coal 0.95–0.97
Wood at 20% moisture: LHV about 14–15 MJ/kg; dry wood about 18–19 MJ/kg
Conventions differ by region and sector: European statistics and engine or turbine efficiencies usually use LHV; US statistics (EIA) and gas billing use HHV. This explains why condensing boilers can be advertised as "107% efficient" on an LHV basis (about 97% HHV) and why a CCGT rated 60% LHV is about 54% HHV. Hydrogen comparisons are particularly sensitive: electrolyser efficiency quoted on HHV appears about 18% higher than on LHV.
Moisture strongly reduces the net value of biomass and lignite. Convert fuel quantities with the fuel energy content calculator.
Related terms
All terms →- Energy density
The amount of energy stored per unit mass (specific energy, Wh/kg or MJ/kg) or per unit volume (Wh/L or MJ/L) of a fuel or storage medium.
- Heat rate
The fuel energy a thermal power plant consumes per kWh of electricity generated; the inverse of efficiency, usually in BTU/kWh or kJ/kWh.
- Natural gas
A fossil fuel composed mainly of methane, used for power generation, industrial and residential heat, and as a chemical feedstock for hydrogen and ammonia.
- Green hydrogen
Hydrogen produced by splitting water in an electrolyser powered by renewable electricity, with near-zero direct CO2 emissions.
- Tonne of oil equivalent (toe)
A conventional energy unit equal to 41.868 GJ (10 Gcal, 11.63 MWh), the nominal heat content of one tonne of crude oil, used in energy balances.
- BTU (British thermal unit)
A traditional unit of heat, approximately the energy needed to raise one pound of water by one degree Fahrenheit; 1 BTU (IT) = 1,055.06 J.