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Heat pump or gas boiler?
Which costs less to run?
Running costs only, for our model house in London. Change the numbers to match your own home. See the answer, and the maths behind it. Nothing you type leaves this page.
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Heat pump against gas boiler: running cost
Start simple. Open Advanced when you want every number.
On these numbers
In our model house the heat pump costs about £44 a year more in energy running costs than the gas boiler on the standard tariff. It would need an SPF of about 2.94 or better to be cheaper.
Energy running costs only, for the numbers set on the left. The line marks the gas boiler. The Cosy bar is a scenario with an assumed split of use, not a forecast.
The same sums for three boiler efficiencies and the three SPF values from the trial: lower quartile, median, upper quartile. Whole pounds a year.
Show the maths
These steps use the numbers set on the left and change as you change them. They are shown so you can check the maths.
What this leaves out
- Installation, grants and servicing. Whether they favour the heat pump or the boiler depends on your quotes, so none is counted.
- Hot water. The SPF in the trial is for the whole heating system. How much of it is hot water was not separated out, so the effect on the result is unknown (?).
- Gas standing charge. A house with a boiler pays it. A house with a heat pump avoids it only if gas is disconnected, which would favour the heat pump by about £110 a year in London. Tick the box in Advanced to see that. The cost of disconnecting is not included (?).
- Electricity standing charge. It is the same with a boiler or a heat pump, so it does not change the difference. Cosy's is about £2 a year lower than the price cap's in London; not counted.
- VAT. Electricity has no VAT until 31 March 2027 and gas has 5%. After that date electricity VAT can only stay at 0% or rise, and a rise would favour the gas boiler. What will happen is not known.
- Your home. Weather, insulation, how you use heat and how your heat pump is installed and set up all move the SPF. A flat Cosy pattern and the assumed 60/40/0 split are examples, not forecasts.
- Prices. All prices are for 1 October to 31 December 2026 and will change.
Example maths. Not financial advice.
Labels: ✓ Documented source and date shown · ◆ Chosen an example value · ? Unknown check the source. How to read them
Sources
What is fact, what is chosen, what is unknown
✓ Documented
- 9,500 kWh of gas a year: Ofgem, review of typical domestic consumption values, decision of May 2026, medium use from 1 July 2026 (Great Britain).
- 26.60p a kWh for electricity and 8.15p for gas, standing charges 42.92p and 30.20p a day: Ofgem price cap tables, London (region C), direct debit, single rate, 1 October to 31 December 2026. Gas includes 5% VAT. No VAT on electricity from 1 October 2026 to 31 March 2027.
- SPF 2.78, and 2.55 to 3.05 for the middle half: Energy Systems Catapult, Electrification of Heat Demonstration Project, summary report, December 2024, page 31 (median seasonal performance of the whole heating system, 428 air-source heat pumps). A government-funded trial of homes fitted in 2020 and 2021, not a random sample.
- Cosy rates in London: 14.12p cheap, 28.80p day, 43.19p peak, 42.29p a day standing charge. Octopus Energy's public price data, product COSY-22-12-08, region C, variable, direct debit, read on 12 November 2026. Hours in GMT: cheap 04:00 to 07:00, 13:00 to 16:00 and 22:00 to 24:00; peak 16:00 to 19:00.
◆ Chosen
- Model house in London. All 9,500 kWh of gas counted as heating and hot water, no gas cooking.
- Gas boiler efficiency 90%. Between 85% and 92% is a sensible range; no measured average for homes was found.
- Cosy scenario: 60% of the heat pump's electricity at the cheap rate, 40% at the day rate, none at the peak rate. An assumption, not a forecast.
- Gas stays connected unless you tick the box.
? Unknown
- Whether Cosy's hours or rates change with the season, and who can sign up for it.
- What it costs to disconnect gas, and other costs that follow.
- The VAT rate on electricity after 31 March 2027.
- How hot water changes the SPF in homes like yours.
Data as of 13 November 2026. Prices change, so check your own. The next Ofgem price cap is expected around 25 November 2026 (to be confirmed); the example prices will then be updated. Found a mistake? See Corrections.
The code, text and images on this site may not be reused without permission. How we work out the numbers.