The sum
A heat pump delivers heat and uses electricity. The ratio between them is its efficiency, so the electricity used is the heat delivered divided by that ratio. The Energy Saving Trust says a heat pump can return three to four times as much heat as the electricity it uses, and that typical systems run at a seasonal figure of around 3.1. The heat your home needs depends on its size, fabric and how you heat it; an installer calculates it room by room during a survey.
This page works through one clearly labelled illustration: a home needing 12,000 kWh of heat a year. That is the same illustrative three-bedroom semi used on the running costs page; it is a model, not a measurement, and your house will differ.
Illustrative figures
| Seasonal efficiency | Electricity for heating (kWh a year) | Cost at 26.32p/kWh |
|---|---|---|
| 2.5 | 4,800 | £1,263 |
| 3.0 | 4,000 | £1,053 |
| 3.5 | 3,429 | £902 |
| 4.0 | 3,000 | £790 |
Price: the Ofgem cap for 1 October to 31 December 2026 is 26.32p/kWh for electricity and 54.83p a day standing charge (GB average, Direct Debit). The standing charge, about £200 a year, is payable whatever you use, so it is excluded from the table. Each 1p/kWh change in your average unit price moves the 3.0 row by about £40 a year. For comparison, the same model puts gas heating at about £1,063 a year on the gas cap rate of 7.97p/kWh, before gas standing charge.
What moves the number
- Heat demand. Insulation, size, glazing and how warm you keep the house all change the 12,000 kWh. The Energy Saving Trust says you do not need lots of insulation to have a heat pump, but a well-insulated home lets it work less. See insulation first?
- Flow temperature and radiators. Larger radiators allow a lower water temperature, and lower is more efficient. See the sizing guide.
- Controls. The heating curve, set-back and boost setting affect how hard the unit works; see the controls guide.
- Hot water. Cylinder size, temperature and the periodic high-temperature cycle (above 60°C) add electricity. The Trust says weekly is safe for most people.
- Weather. A colder winter means a lower COP and more heat needed.
From kWh to your bill
The electricity line goes up and, if you are replacing gas or oil, the other line goes down. The Trust says that when replacing a gas boiler, if you can remove gas altogether you also lose the gas standing charge, about £108 a year at the current cap, and that if you are replacing electric heating your electricity costs should fall considerably. The tariff matters too: a time-of-use tariff can lower the average unit price if you shift hot water and some heating to cheap periods, though it can charge more at other times, so check it against how you live. See heat pump tariffs. Use the calculator with your own figures.
Your electricity use and running cost
No details needed. Change any figure to match your own quote or bills. Results are indicative — an MCS installer’s heat-loss survey and written quote are what count.
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Difference per year at these prices.
Prices: Ofgem cap 1 October to 31 December 2026 — electricity 26.32p/kWh, gas 7.97p/kWh, gas standing charge 29.68p/day (GB average, Direct Debit); heating oil 114.8p/litre including 5% VAT (109.3p before VAT; BoilerJuice UK average for 1,000 litres, read 28 September 2026); 10.35 kWh per litre assumed. No VAT on household electricity from 1 October 2026 to 31 March 2027, which flatters heat pumps in this window. LPG prices vary too much to default — use your own bills. Illustrative, not a quote.
How much does a heat pump cost per hour?
It depends on how hard it is working, which changes with the weather, so there is no single hourly figure. The arithmetic is simple: the cost of an hour is the electricity drawn in that hour times the price. At the Ofgem cap for 1 October to 31 December 2026 (26.32p per kWh), every kilowatt of electricity drawn for an hour costs about 26.3p.
As an illustration, DESNZ reports a median air source heat pump size of 8 kW of heat output for grant-funded jobs in 2026 Q3. A system that size running flat out at an efficiency of 3 would draw about 2.7 kW of electricity, about 70.2p an hour; on a cold day at the trial’s minus 5°C efficiency of 2.3, about 91.5p. Most of the year it runs well below full output, so the typical hour costs less. For a year’s figure, the heat pump running cost calculator takes your own heat demand and tariff.
How to get your own figure
- Ask each installer for the annual heat demand from the heat-loss calculation, and the seasonal efficiency they assume with the flow temperature behind it.
- Divide one by the other and check it matches their predicted electricity use.
- Compare to your current fuel spend over twelve months, using actual bills.
- Check your meter type and tariff before the survey; the Trust says smart meters can open up more tariffs.
Put these answers next to the quote totals using the quotes checklist, and use the worth-it guide to judge what the running cost means for your situation.