1. The short answer
Net calorific value (NCV, called Hu in Germany) and gross calorific value (GCV, called Ho) describe the same combustion energy two different ways: net value counts only the "dry" heat of combustion, gross value also counts the heat recovered when the water vapour in the exhaust condenses, which is why German heating oil EL is rated at 10.6 kWh per litre gross against 9.8 kWh per litre net (heizwert.info, accessed 18 September 2026). What matters for you is neither label on its own, but the price per kilowatt-hour: only once you divide your price per litre, kilogram or cubic metre by the right energy content do heating oil, gas and pellets actually become comparable.
This page sets out the figures for common fuels, works through a current German price example, and keeps calorific value strictly separate from your boiler's efficiency, so the comparison is not distorted.
2. How net and gross calorific value are set
The difference is physical, not a matter of opinion: burning heating oil, gas or pellets produces water vapour, and net calorific value (NCV) writes off the condensation heat in that vapour as it escapes up the flue, while gross calorific value (GCV) counts it in full. How large the gap is depends on the fuel's hydrogen content; for heating oil EL, heizwert.info puts it at roughly 0.8 kWh per litre, between 9.8 kWh (NCV) and 10.6 kWh (GCV), as of 18 September 2026.
What minimum value heating oil EL must reach is set by a product standard: low-sulphur heating oil must reach a net calorific value of at least 42.6 MJ/kg under Germany's DIN 51603-1 (VIA-Energy product specification, July 2019, per DIN 51603-1). The standard sets that minimum on the net basis; it does not set one on the gross basis, which instead matters mainly for how condensing-boiler efficiency gets labelled.
3. Energy content and price per kWh, side by side
The figures below come from a single German reference source for energy content, and Germany's daily heating oil price for the price example; both are shown with their own date rather than averaged.
| Fuel | Value | Date | Source |
|---|---|---|---|
| Heating oil EL, net (NCV) | 9.8 kWh/l, or 11.9 kWh/kg | accessed 18 Sep 2026 | heizwert.info |
| Heating oil EL, gross (GCV) | 10.6 kWh/l | accessed 18 Sep 2026 | heizwert.info |
| Natural gas H | roughly 10.4 kWh/m³ | accessed 18 Sep 2026 | heizwert.info |
| Wood pellets | roughly 4.9 kWh/kg | accessed 18 Sep 2026 | heizwert.info |
| LPG (propane) | roughly 12.9 kWh/kg | accessed 18 Sep 2026 | heizwert.info |
| Electricity | 1 kWh = 1 kWh, no conversion loss like NCV/GCV fuels | as of 18 Sep 2026 | own framing |
| German heating oil price | 181.0 cents/litre for 3,000 L | 17 Sep 2026 | Tecson |
| Price per kWh, net basis | roughly 18.5 cents/kWh (181.0 ct/l ÷ 9.8 kWh/l) | 17 Sep 2026, own calc | own conversion |
| Price per kWh, gross basis | roughly 17.1 cents/kWh (181.0 ct/l ÷ 10.6 kWh/l) | 17 Sep 2026, own calc | own conversion |
No current, dated retail price for natural gas or wood pellets was found in this research, so no price per kWh is calculated for those fuels here; the same formula, price per litre, kilogram or cubic metre divided by the fuel's kWh content, applies just as well to your own supply contract, whichever fuel it covers. How the daily heating oil price itself is set is explained in our heating oil price entry.
4. Which basis counts, and why condensing boilers show over 100%
For comparing your own price per kilowatt-hour, knowing which basis a supplier uses matters more than insisting on one figure over the other. Heating oil dealers almost always quote energy content on a net basis (9.8 kWh/l), because that is the reference value written into the product standard; use the gross figure (10.6 kWh/l) instead and you get a lower price per kilowatt-hour automatically, without heating oil actually becoming cheaper (own calculation from heizwert.info and Tecson, as of 18 September 2026).
That is also why manufacturers can rate a condensing boiler's efficiency above 100 percent: the percentage is measured against net calorific value, the ceiling an older standard boiler used, while a condensing unit additionally recovers condensation heat from the flue gas. No boiler, however efficient, physically exceeds the gross calorific value itself, whatever percentage sits on the nameplate. Boiler efficiency is a property of the heating system, calorific value is a property of the fuel, and the two figures need to stay separate or the price comparison gets distorted. How bio-blend content changes that fuel-side energy figure is covered in our bioheat and HVO entry. How carbon costs are assessed against that same energy content is covered in our carbon tax entry.
5. What this means for comparing your heating oil, gas or pellet bill
Never compare offers by price per litre, kilogram or cubic metre alone, always convert to price per kilowatt-hour, and on the same basis. The formula is simple: price per litre, kilogram or cubic metre divided by the fuel's kWh content gives you the price per kilowatt-hour of fuel energy. In the German example from 17 September 2026, that works out to roughly 18.5 cents per kWh on a net basis for heating oil EL at 181.0 cents per litre (Tecson; own calculation).
What matters for your own bill: that price per kilowatt-hour is the price for the energy in the fuel, not yet the price for the heat that actually reaches your radiators. For that, you also need your boiler's efficiency, which only the manufacturer or a certified technician can state reliably. Run both figures through our calculator to compare offers across fuels on a fair basis. Our buy now or wait page for the US Northeast shows how to weigh that price against timing.
Compare heating oil, gas and pellets fairly, on price per kilowatt-hour.
Run the calculator6. Misconceptions: what NCV and GCV do NOT mean
A condensing boiler rated at more than 100 percent efficiency is not creating energy from nothing, that percentage is measured against net calorific value as a reference point, not against total physical energy content. No boiler exceeds gross calorific value (GCV) itself, that would break the conservation of energy.
Also commonly confused: boiler efficiency is a property of the heating system, not of the fuel. A higher calorific value per kilogram does not automatically make a fuel cheaper, that depends entirely on the price per kilowatt-hour. And heating degree days say nothing about your fuel's energy content, they only describe how cold the winter actually was. Similarly, how long stored heating oil lasts has nothing to do with its calorific value, ageing fuel loses quality, not automatically energy content.