Air to air heat pumps in London

Both types take heat from the outside air. The difference is how they deliver it.

| | Air to air | Air to water | |---|---|---| | Heats | the room air through indoor units | water for radiators or underfloor heating | | Hot water for taps | usually not | yes, through a cylinder | | Cooling | yes | rarely in UK homes | | Needs radiators | no | yes, often larger ones | | BUS grant | £2,500 (eligible homes) | £7,500 |

The Energy Saving Trust notes that air to air systems can suit smaller homes and flats, and that most do not provide hot water, so you will need another way to heat water, such as a cylinder with an immersion heater or an electric shower.

This changed in 2026, so check the latest before you sign. The government's Boiler Upgrade Scheme page now lists £2,500 towards an air to air heat pump, alongside £7,500 for air to water and ground source. Ofgem's rules say:

• the installer must be certified by the Microgeneration Certification Scheme (MCS)
• the property must be in England or Wales, and air to air grants are for homes, not non residential buildings
• the new system must replace fossil fuel or electric heating, not another low carbon system
• it must be sized to meet the home's full space heating needs
• new builds (apart from some self builds) and social housing are excluded

The catch is timing. As of 20 October 2026 the Energy Saving Trust says there are no MCS certified installers for air to air heat pumps yet, and MCS expects certification before the end of 2026. Until then, a grant funded air to air install is not possible. You can still pay for one yourself.

In England, a heat pump can be permitted development under Class G as long as it is not used solely for cooling and meets the size, siting and noise rules. A reversible system installed to heat your home sits much more comfortably within those rules than a cooling only air conditioner. The outdoor unit must still meet the 37 dB(A) noise calculation at your neighbour's window, and flats, listed buildings and street facing walls in conservation areas still need consent.

Air to air tends to work well in flats heated by electric panel or storage heaters, in small homes, and in houses that want cooling as well as heat. It suits people who are happy with warm air from wall units rather than radiators. It is less suited to large, draughty homes with high heat loss, or households that want one system for heating and hot water. Good insulation and draught proofing help any heat pump. There is not much UK data yet on how air to air systems perform in homes, so ask any installer to explain their running cost estimate for your design.