Almost every fuel-energy figure comes in two flavours that differ by several percent, and confusing them is one of the most consequential errors in this domain. The two flavours are the higher heating value and the lower heating value.
The two bases
- Higher / gross heating value — HHV, also GCV; in German, Brennwert. It includes the latent heat released when the water vapour produced by combustion condenses back to liquid.
- Lower / net heating value — LHV, also NCV; in German, Heizwert. It excludes that latent heat, assuming the water leaves as vapour and its heat is not recovered.
The higher value is always the larger of the two, because it counts extra heat the lower value ignores. The size of the gap depends on how much hydrogen and moisture the fuel contains — the more water vapour combustion produces, the wider the gap.
How big is the gap?
- For natural gas, HHV exceeds LHV by roughly
~5–6%. - For hydrogen and wet biomass, the gap can reach
~10–20%.
These are not rounding errors — a 5–20% swing changes a result meaningfully. Quoting a value on one basis while the reader assumes the other is a real mistake, not a nuance.
How the tool handles it
The tool defaults to LHV/NCV, the dominant convention in international energy statistics (the IEA/OECD balances and the toe definition itself are on a net basis). Beyond that:
- Every fuel-energy result labels its basis — the basis is never omitted.
- Where the data has an HHV/GCV value too, it is shown alongside as a labeled secondary figure, never mixed in silently.
- The tool never derives one basis from the other by a generic factor, because the LHV→HHV gap depends on the specific fuel. If only one basis is in the data, the other is shown as "not available".
Why it matters for bills
Conventions clash in the real world. UK gas billing and DESNZ/DEFRA guidance default to the gross (GCV/HHV) basis, so the energy on a UK gas bill is gross even though many emission factors are published per gigajoule on a net basis. That kind of mismatch is exactly what the tool surfaces rather than hides. See natural gas: m³ to kWh and why fuel conversions are approximate for how basis interacts with the rest of the fuel calculation.