Work out natural gas heating value instantly with clear inputs, formula shown and shareable results.
Heating value is the mole-weighted sum of component heating values: methane 37.71 MJ/m3 gross, ethane 66.07 and propane 93.94, with nitrogen and carbon dioxide contributing nothing. The Wobbe index, heating value divided by the square root of relative density, governs burner interchangeability and is the specification that matters for appliances.
Heating value
HHV = sum of mole fraction x component gross heating value
Wobbe index
Wobbe = HHV / sqrt(relative density)
Gas is usually sold on gross (higher) heating value, which counts the latent heat of the water formed. Efficiency of appliances that do not condense the flue gas should be assessed on net.
Burners are set for a heat input at a given pressure. Two gases with the same heating value but different density deliver different heat through the same orifice; the Wobbe index captures that combined effect.