Heating cost comparison: cost per useful kWh for every fuel

How this heating cost comparison works

Heating fuels are sold in units that don’t compare: kWh of gas, litres of oil or LPG, tonnes of pellets, steres of firewood. They are then burned in appliances with very different efficiencies. So the price on the invoice tells you almost nothing. What counts is the cost of each kWh of heat that actually reaches your rooms.

This calculator puts nine systems on the same footing:

1. It converts each price into cost per kWh of fuel, using the energy content of one unit (for example 10.35 kWh per litre of heating oil, 4.8 kWh per kg of pellets).
2. It divides by the seasonal efficiency of the appliance (90% for a condensing gas boiler, 72% for a log stove). For heat pumps it divides by the SCOP, which is above one because a heat pump moves ambient heat instead of creating it.
3. It multiplies the resulting cost per useful kWh by your annual heat demand to get a yearly bill, adds an optional gas standing charge and typical servicing costs, and ranks the results.
4. It estimates the fuel quantity you’d need and the CO₂ each option emits, with official emission factors for fossil fuels and your grid’s intensity for electricity.

The formula

Energy contents used (gross): LPG 7.08 kWh/L, heating oil 10.35 kWh/L, pellets 4.8 kWh/kg, seasoned hardwood about 1,700 kWh per stere (editable). Emission factors: gas 0.183, LPG 0.214, oil 0.247 kg CO₂/kWh (UK DESNZ 2024, gross basis). For wood only supply-chain emissions are counted.

Worked example

The defaults describe a house that needs 15,000 kWh of useful heat a year, with electricity at €0.28/kWh and gas at €0.10/kWh. The ranking:

The electricity-to-gas price ratio here is 2.8, well under the 3.56 break-even point for an air-source heat pump, so it saves about €354 a year compared with gas. Direct electric heating costs four times as much as the cheapest option. On CO₂, wood pellets (0.51 t/yr) and logs come lowest. The heat pumps emit 1.3–1.6 t on a 350 g/kWh grid, gas 3.05 t and oil 4.2 t.

How to read the results

• The big tile is the cheapest option. The other tiles show each system’s annual cost and how much more it costs than the cheapest.
• Heat pump vs gas price ratio compares your prices with the break-even ratio (SCOP ÷ boiler efficiency). Below it, the heat pump is cheaper to run.
• The ranked bar chart makes the gaps obvious, and the CO₂ chart runs from cleanest to dirtiest.
• The table lists the fuel price per kWh, efficiency, cost per useful kWh and the amount of fuel you’d buy. Handy when sizing an oil tank or pellet store.

Typical values

Tips to lower your heating cost

• Reduce demand first. Every option scales with heat demand, so insulation cuts every bill. Try the insulation savings calculator.
• Check your price ratio. If electricity costs less than three times the gas price, a heat pump will almost certainly be cheaper to run. Look at it in detail with the heat pump calculator.
• Count fixed costs. Leaving gas altogether saves the standing charge, often €100–200 a year. Enter it in the advanced options.
• Buy seasoned wood. Wet wood (over 25% moisture) can give a third less heat per stere and soots up chimneys.
• Think in lifetime costs. Running costs are only half the picture. The heat pump vs gas boiler calculator adds installation, maintenance and replacements over 15 years.

Limitations

Seasonal efficiencies and SCOP values are typical figures; a badly commissioned heat pump or an oversized boiler can do 10–20% worse. Installation, replacement and financing costs are left out, so the ranking covers running costs only. The energy content of wood varies a lot with species and moisture. Electricity CO₂ uses a single average grid factor, while real marginal emissions change by hour and season. For a dedicated wood boiler analysis see the biomass boiler calculator.

Method & assumptions

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