Air-to-Air vs Air-to-Water Heat Pumps: Which Should You Choose?
The difference between air-to-air and air-to-water heat pumps — heating, cooling, hot water, radiators and the Boiler Upgrade Scheme grant for each — and which suits your home.
By Max Tuleberg · Founder, Vento · Last updated 25 October 2026
Founder of Vento. Worked on the tools before building the software.
Air-to-air heat pumps heat and cool your rooms with warm or cool air — they're what most people call air conditioning. Air-to-water heat pumps heat water for radiators, underfloor heating and usually your hot water. Both can replace a gas or oil boiler and both can get a Boiler Upgrade Scheme grant in England and Wales, but they suit different homes.
Side by side
| Air-to-air | Air-to-water | |
|---|---|---|
| Heats | Room air, through indoor units | Water for radiators or underfloor heating |
| Cools in summer | Yes | Not through ordinary radiators |
| Hot water | No — needs a separate solution | Usually, via a cylinder |
| Uses your radiators | No | Yes (they may need upsizing) |
| Boiler Upgrade Scheme grant | £2,500, homes only | £7,500 (+£1,500 off-gas uplift for a limited period) |
| Minimum efficiency for the grant | No SCOP floor | SCOP 2.8 |
| Disruption | Usually a day or two per system | Larger — cylinder, pipework, often radiators |
Choose air-to-air if…
- You want cooling in summer as well as heating.
- You heat a few main rooms and want a smaller, quicker install.
- Your hot water is already sorted another way (for example an electric cylinder).
Choose air-to-water if…
- You want to keep heating through radiators or underfloor heating.
- You need the heat pump to provide your hot water too.
- You want the larger grant and are prepared for a bigger job.
The grant
Both qualify for the Boiler Upgrade Scheme in England and Wales when they replace fossil-fuel or electric heating and are fitted by an MCS-certified installer. Air-to-air gets £2,500 and is for homes only; air-to-water gets £7,500. Use the grant checker to see whether your home is likely to qualify, or read how the air conditioning grant works.
This guide is general information for UK installers, not legal or regulatory advice. Always check the current regulations and manufacturer instructions for your specific job.
Frequently asked questions
What is the difference between air-to-air and air-to-water heat pumps?
An air-to-air heat pump heats (and cools) rooms directly by blowing warm or cool air from indoor units — it is what most people call air conditioning. An air-to-water heat pump heats water for your radiators or underfloor heating and usually your hot water cylinder too. It can't cool through ordinary radiators.
Does an air-to-air heat pump provide hot water?
No. An air-to-air system heats and cools the air in your rooms but doesn't heat water, so you'll still need another way to heat hot water, such as an electric immersion or a separate hot water heat pump.
Which heat pump gets the bigger grant?
Under the Boiler Upgrade Scheme in England and Wales, an air-to-water heat pump gets £7,500 (plus £1,500 for homes off the gas grid on oil or LPG, for a limited period), and an air-to-air heat pump gets £2,500. Air-to-air is residential only and has no off-gas uplift.
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