Fuel Properties
Heating values in MJ/kg. LHV (net) excludes the latent heat of the water formed by combustion; HHV (gross) includes it. Europe quotes efficiency against LHV and the US against HHV, which is why the same boiler is "92% efficient" in one market and "83%" in the other — and why a condensing appliance can legitimately exceed 100% on a net basis.
| Fuel | LHV (MJ/kg) | HHV (MJ/kg) | LHV/HHV | Stoich. A/F (mass) | Max dry CO₂ (%) | kg CO₂ / kg fuel |
|---|---|---|---|---|---|---|
| Natural gas (as methane) | 50.0 | 55.5 | 0.901 | 17.19 | 11.74 | 2.74 |
| Propane | 46.4 | 50.4 | 0.921 | 15.63 | 13.76 | 2.99 |
| Butane | 45.8 | 49.5 | 0.925 | 15.42 | 14.06 | 3.03 |
| Petrol (as octane) | 44.3 | 47.3 | 0.937 | 15.09 | 14.55 | 3.08 |
| Diesel (as cetane) | 42.7 | 45.6 | 0.936 | 14.92 | 14.80 | 3.11 |
| Light fuel oil | 42.6 | 45.4 | 0.938 | 14.63 | 15.24 | 3.16 |
| Methanol (CH₃OH) | 19.9 | 22.7 | 0.877 | 6.45 | 15.06 | 1.37 |
| Ethanol (C₂H₅OH) | 26.8 | 29.7 | 0.902 | 8.98 | 15.06 | 1.91 |
| Hydrogen | 120.0 | 141.8 | 0.846 | 34.19 | 0.00 | 0.00 |
Maximum dry CO₂ occurs at exactly stoichiometric; every combustion analyser reading is measured against it, which is why the instrument has to be told the fuel. Work out excess air, flue loss and boiler efficiency from a real analyser reading on the Combustion & Flue Gas tool. Values are for representative compositions — natural gas in particular varies by supply, so use a gas analysis where the number matters commercially.
A reference aid, not a substitute for engineering judgment. Verify against the governing standard.