Glossary · Heat pumps, grants and regulations
What is an air to water heat pump?
An air to water heat pump takes heat from the outside air using electricity and passes it to your central heating and hot water. It works a little like a fridge in reverse. MCS says it is the most common type of air source heat pump in the UK, and it can work with radiators or underfloor heating.
Key points
- It moves heat from outdoor air into your heating water, rather than making heat by burning fuel. MCS says it can still produce heat at minus 15 degrees outside.
- The Boiler Upgrade Scheme currently gives £7,500 towards an air source heat pump, with an extra £1,500 for oil and LPG homes until March 2027.
- MCS gives the average cost of an air source heat pump as around £13,300 in 2025, before any grant.
- A newly installed or fully replaced wet heating system should be sized to work at a flow temperature of 55°C or lower where feasible.
- MCS says an air source heat pump lasts up to 20 years on average and should have a yearly check-up by a professional.
How an air to water heat pump works
An air source heat pump transfers heat from outside your home into your home using electricity, rather than generating the heat itself. MCS says it works like a fridge in reverse. The unit absorbs heat from the outside air and passes it at low temperature to the compressor. That raises the temperature and a condenser transfers the heat to your heating and hot water. MCS says this can still generate heat when it is minus 15 degrees outside.[1]MCS, Air Source Heat Pump
There are two main kinds of air source heat pump. In an air to water system the heat goes into water, which can be held in a storage tank or sent to radiators or underfloor heating. MCS says it is the most common option in the UK. An air-to-air heat pump instead uses fans to circulate warm air and does not provide hot water.[1]MCS, Air Source Heat Pump
All air source heat pumps run on electricity. MCS says the heat produced is more than the electricity needed to power them.[1]MCS, Air Source Heat Pump Manufacturers publish efficiency figures, which our page on COP and SCOP explains. The unit is installed outside, on a wall or on the ground, and needs enough space around it for airflow.[1]MCS, Air Source Heat Pump
What the rules and grants say
| Topic | Position |
|---|---|
| Grant | £7,500 through the Boiler Upgrade Scheme. Extra £1,500 until March 2027 for oil or LPG homes with no mains gas. No grant for hybrid systems |
| Capacity | The scheme covers individual systems up to 45kWth |
| Installer | The grant goes through an MCS certified installer |
| Flow temperature | A new or fully replaced wet system should be designed for a maximum flow temperature of 55°C or lower where feasible |
| Sizing | Heat pumps should be selected to meet the full space heating requirement at the design condition used for the heat loss calculation |
| Commissioning | Commissioned to the manufacturer’s instructions and the system design parameters |
The grant figures come from GOV.UK.[2]GOV.UK, Apply for the Boiler Upgrade Scheme: What you can get The design and commissioning points come from Approved Document L.[3]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments It says that where it is not feasible to reach a 55°C flow temperature, for example because there is not enough space for larger radiators, the system should be designed to the lowest design temperature that will still meet the home’s heating needs.[3]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments
The Heating and Hotwater Industry Council says that for monoblock units, all the refrigerant is sealed within the outdoor unit, so installers do not need F-gas qualifications. Systems that carry refrigerant between indoor and outdoor units need F-gas qualified engineers.[4]Heating and Hotwater Industry Council, Air-to-air heat pumps added to Boiler Upgrade Scheme
Cost, space and servicing
MCS puts the average cost at around £13,300 in 2025, depending on the size and age of the property and the type of heat pump.[1]MCS, Air Source Heat Pump You do not need a big garden. MCS says most properties have enough space, and that changes to permitted development rights eased planning restrictions from 20 September 2025 in England and 1 June 2026 in Wales.[1]MCS, Air Source Heat Pump
On average MCS says an air source heat pump lasts up to 20 years, and recommends a yearly check-up by a professional. It also advises removing any plants growing near the unit, as they can affect performance.[1]MCS, Air Source Heat Pump BASI lists a heat pump annual service as a fixed £200, with about two hours on site, and installs MCS certified air source heat pumps with the Boiler Upgrade Scheme application made for you.[5]BASI Heating, Air source heat pumps, grant applied for you See our heat pump page.
Example
Mark lives in a mid-terrace in Keighley with a gas combi boiler. He asks BASI about a heat pump. After a survey the installer checks whether his radiators can heat the house at a low flow temperature and whether the cylinder and outdoor unit have space. Mark chooses an air to water system. The installer applies for the £7,500 grant, shows it on the quote and takes it off the invoice. Mark keeps the MCS certificate and handover pack.
What people get wrong
Many people think a heat pump cannot work in a cold British winter. MCS says an air source heat pump can still generate heat when it is minus 15 degrees outside. The better question is whether your radiators and insulation suit a lower flow temperature.
The second mistake is to treat all heat pumps alike. An air to water system feeds radiators or underfloor heating, while an air-to-air system warms air and does not provide hot water. The grant is not the same either: £7,500 for air to water, £2,500 for air-to-air.[2]GOV.UK, Apply for the Boiler Upgrade Scheme: What you can get
The bottom line
An air to water heat pump takes heat from outside air and uses electricity to raise it to heat radiators and hot water. The Boiler Upgrade Scheme currently gives £7,500 towards it, and MCS puts the average cost at around £13,300. Your home needs a survey so the system is sized properly and can run at a low flow temperature. Compare it with ground source before you decide.
Common questions
How does an air to water heat pump work?
An outdoor unit absorbs heat from the air and passes it to a compressor, which raises its temperature. A condenser then transfers that heat to your heating and hot water. The heat delivered is more than the electricity used to run it.
How much is the grant for an air to water heat pump?
GOV.UK currently lists £7,500 through the Boiler Upgrade Scheme for an air source heat pump. Until March 2027 there is an extra £1,500 for homes heated by oil or LPG with no mains gas. Hybrid systems are not eligible.
How much does an air to water heat pump cost?
MCS puts the average cost of an air source heat pump at around £13,300 in 2025, depending on the size and age of the property and the heat pump type. BASI quotes a fixed price after a survey.
Do I need planning permission?
MCS says changes to permitted development rights eased planning restrictions for air source heat pumps from 20 September 2025 in England and 1 June 2026 in Wales. Check with your installer or local council for your property.
Sources
We cite the original source for every figure: government, regulators, standards bodies and manufacturers' own documents. Each one shows the date we last checked it.
- MCS. Air Source Heat Pump. Checked 11 November 2026. ↩
- GOV.UK. Apply for the Boiler Upgrade Scheme: What you can get. Checked 11 November 2026. ↩
- Ministry of Housing, Communities and Local Government. Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments. Checked 11 November 2026. ↩
- Heating and Hotwater Industry Council. Air-to-air heat pumps added to Boiler Upgrade Scheme. Checked 11 November 2026. ↩
- BASI Heating. Air source heat pumps, grant applied for you. Checked 11 November 2026. ↩