The comparison boundary
All selected heating systems supply the same useful heat demand. We compare the energy cost per useful kWh and the annual running cost for that demand. This is a running-cost model, not a building heat-loss survey, equipment sizing calculation or full investment appraisal.
Formulas
| Source | Energy-only cost per useful kWh |
|---|---|
| Heat pump / heating AC | Electricity price per kWh ÷ SCOP or COP |
| Gas boiler | Gas price per unit ÷ (kWh per gas unit × efficiency) |
| Electric resistance heater | Electricity price per kWh |
| Wood / pellets | Fuel price per unit ÷ (kg per unit × kWh/kg × efficiency) |
Efficiencies entered as percentages are divided by 100. Annual energy cost is useful heat demand multiplied by the energy-only cost per useful kWh. We add the annual fixed-cost allowance you enter for each selected source. Monthly figures are annual totals divided by twelve, not weather-adjusted monthly predictions.
Heat-demand options
- Useful heat: the annual heat demand you enter directly.
- From gas use: annual gas units × kWh per gas unit × boiler efficiency. Include only consumption serving the demand you want to compare.
- Electric heater schedule: electrical input kW × hours per day × days per year × average power fraction, assuming resistance heating.
Unit conversions
One ft³ = 0.028316846592 m³. One lb = 0.45359237 kg. One metric tonne = 1,000 kg. We use 29.307107 kWh per therm. For volumetric gas tariffs, enter your effective billing kWh per m³. Wood mass per m³ must match how the purchased load is measured.
Break-even calculation
Energy-only break-even COP = electricity price per kWh ÷ gas cost per useful kWh. This excludes fixed costs. The annual ranking includes the fixed costs you enter, so it can differ from the energy-only comparison. A zero gas energy price has no finite break-even value; no threshold is shown in that case.
Assumptions and exclusions
- Default prices and performance values are illustrative inputs, not live tariffs or national averages.
- Currency selection changes the label only. Enter every price in the same currency; use £0.30 for 30p.
- Fuel energy and appliance efficiency must use a consistent gross or net calorific basis.
- SCOP and COP are supplied by you. The calculator does not infer performance from weather.
- Negative tariffs and efficiencies over 100% for boilers or stoves are outside this model.
- Purchase price, installation, grants, financing, emissions and comfort differences are excluded.
- Auxiliary electricity, standing charges and maintenance are included only if you allow for them in your inputs or annual costs.
- Displayed values are rounded; comparisons use unrounded calculations.
Background sources
The arithmetic above is implemented directly in our calculator. These references provide background and input guidance; they do not certify this website or its default assumptions.
- Energy Saving Trust: air source heat pumps
- Energy Saving Trust: air-to-air heat pumps
- GOV.UK: gas meter readings and bill calculation
Method version 2.0.0, published 19 September 2026. Found an error? Send the inputs and the result so it can be reproduced and checked.