What decides the running cost
Three numbers set the bill. None of them is a national average.
- How much heat your home needs. A larger or draughtier house needs more heat, whatever supplies it. This is measured in kilowatt-hours (kWh) a year.
- How efficient the heat pump is over the year. Installers call this the seasonal efficiency, or SCOP. A figure of 3 means three units of heat for each unit of electricity.
- What you pay for electricity. The unit rate on your tariff, in pence per kWh.
Put together:
The running cost sum
Annual running cost = heat needed ÷ seasonal efficiency × electricity unit rate.
A home that needs 12,000 kWh of heat a year, with a heat pump achieving a seasonal efficiency of 3, uses 4,000 kWh of electricity for heating. Multiply that by your own unit rate to get the cost.
The example is only to show the sum. Use the figures for your own home, which the next section explains how to find.
Where to find your own numbers
- Heat needed. An installer’s room-by-room heat-loss calculation gives the most reliable figure. An Energy Performance Certificate also lists the estimated energy needed for heating and hot water.
- Seasonal efficiency. A quote from an MCS-certified installer should come with a performance estimate, showing the efficiency the design is expected to achieve and the electricity it is expected to use in a year.
- Electricity unit rate. On your bill or your supplier’s tariff page. Note the standing charge separately: you pay it whether or not you have a heat pump.
Heat pump or gas boiler: the break-even test
Electricity costs more per unit than gas, so a heat pump has to be efficient enough to make up the difference. The test is simple:
The break-even test
A heat pump is cheaper to run than a gas boiler when its seasonal efficiency is higher than (electricity unit rate ÷ gas unit rate) × the boiler’s efficiency.
The table shows what that means at different price gaps. It assumes the boiler turns 90% of its gas into useful heat. It is arithmetic, not a forecast, so put your own rates in.
| If electricity costs… | the heat pump needs a seasonal efficiency above… |
|---|---|
| 3 times as much per unit as gas | 2.7 |
| 3.5 times as much | 3.15 |
| 4 times as much | 3.6 |
| 4.5 times as much | 4.05 |
Two things sit outside that sum. If the heat pump replaces the last gas appliance in the home, you can ask your supplier about removing the gas meter, which ends the gas standing charge. And a time-of-use tariff lowers the average price you pay for the heat pump’s electricity, which lowers the efficiency it needs to break even.
Our heat pump vs gas boiler guide compares the two systems more widely.
Compared with oil, LPG and electric heating
- Oil and LPG. The same test applies, using what you pay per unit of heat from your current fuel. Prices for both move a lot, so check with recent bills.
- Direct electric heaters. Panel heaters and electric boilers give one unit of heat for each unit of electricity. A heat pump gives several, so for the same warmth on the same tariff it uses a fraction of the electricity.
- Storage heaters. These use cheaper overnight electricity, so the comparison depends on your tariff. Our guide to replacing storage heaters with a heat pump covers it.
What keeps the bill low
A low water temperature
This is the biggest single factor. The cooler the water a heat pump has to produce, the less electricity it uses. A system designed to heat the home with water at 40°C is noticeably more efficient than one that needs 55°C. Correctly sized radiators, or underfloor heating, are what make the lower temperature possible.
Weather compensation
Most heat pumps can lower the water temperature automatically on milder days. Make sure it is set up at handover, and resist turning the temperature up to make the radiators feel hotter. Warm rooms from lukewarm radiators is the system working as designed.
Steady running
Keep the house at an even temperature, with a small setback at night, rather than letting it go cold and reheating it fast. Fast reheating needs hotter water, which costs more.
Sensible hot water settings
Heating the cylinder takes a higher temperature than heating the radiators. Storing water no hotter than you need, and heating it at cheaper times if your tariff has them, keeps that part of the bill down. Follow your installer’s advice on the periodic hot water hygiene cycle.
The right tariff
Compare tariffs once the heat pump is in. A time-of-use tariff can help where hot water and some heating can move to cheaper hours. Look at the peak rate and standing charge as well as the cheap rate.
Insulation and draught-proofing
Every unit of heat the house does not lose is a unit you do not pay for, and a home that loses less heat can run at a lower water temperature. Our insulation grants page lists the schemes that can help.
Solar panels
Solar panels will not cover winter heating, when the heat pump works hardest, but they can supply hot water and some heating in spring and autumn. See our solar panels page.
Why the installed cost matters too
Running cost is only half the picture. What you pay to install the system, after the grant, is the other half. Our heat pump grants page sets out the grant values and what you would still pay.
Questions to ask an installer
Before you accept a quote
- What water temperature is the system designed to run at on a cold day?
- What seasonal efficiency does the performance estimate show, and how much electricity a year?
- Which radiators are changing, and what would the efficiency be if they did not?
- Will weather compensation be set up and explained at handover?
- If a saving is quoted, which unit rates and standing charges was it worked out with?
We do not publish savings figures. A defensible one has to be worked out for your property and your tariff, which is what the sums on this page are for.
Check your property
Three quick answers take you to our eligibility check with them already filled in. It is free, and nothing is sent until you choose to send it.
