A heat pump is an electrically powered system that collects low-temperature heat from outside a building, from the air, the ground or water, raises its temperature and releases it indoors for space heating and, in most systems, hot water. Because it moves heat rather than making it by burning fuel, it can deliver several units of heat for each unit of electricity it uses.
How it works
A heat pump works like a fridge in reverse. A refrigerant flowing through a closed loop absorbs heat from the outside source and evaporates. A compressor squeezes the gas, which raises its temperature. The hot refrigerant then passes its heat to the radiators, underfloor heating or hot water cylinder, condenses, and the cycle repeats. A heat pump can still extract heat when the outside air is below freezing, although it works harder in cold weather.
| Type | Heat source | Delivers | BUS grant (England and Wales) |
|---|---|---|---|
| Air-to-water (air source) | Outdoor air, via a fan unit | Radiators, underfloor heating, hot water | £7,500 |
| Ground source | Pipes in horizontal trenches or vertical boreholes | Radiators, underfloor heating, hot water | £7,500 |
| Air-to-air | Outdoor air | Warm air through indoor units; no hot water | £2,500 |
Ground source systems draw on ground temperatures that change less through the year than air temperatures, but the groundworks make them more expensive to install.
UK numbers
- Between May 2022 and 31 August 2026, 93,364 Boiler Upgrade Scheme vouchers were redeemed in England and Wales, according to Ofgem. The scheme also funds biomass boilers, so not all of these are heat pumps.
- To qualify for that grant, an air-to-water or ground source heat pump must have a seasonal coefficient of performance (SCOP) of at least 2.8 and, for most single systems, a capacity of no more than 45 kW thermal.
Why it matters
A heat pump burns no fuel on site. It runs on electricity, so their emissions fall as more of the grid’s power comes from renewables. Running costs depend on how efficient the installation is and on the relative price of electricity and gas. Grant rules change, so check GOV.UK for the current position; this is general information, not advice.
Read more: Renewable energy at home: what works in a UK house.