Air-to-Air vs Air-to-Water Heat Pumps

Air-to-water heat pumps transfer heat from the outside air into water, which then runs your radiators or underfloor heating and provides hot water. They are the direct replacement for a gas, oil or LPG boiler, and they suit a whole-house retrofit.

Air-to-air systems move heat straight into the air of the room through indoor units. They do not give you hot water, but they do something an air-to-water system cannot: run in reverse in summer and cool the room. That is one machine covering both ends of the year.

Which one fits depends on the building. Air-to-air tends to win for extensions, garden rooms, conversions and rooms that overheat badly in summer, and it is far less disruptive to install because there is no wet system to reconfigure. Air-to-water wins where you are replacing a boiler outright.

Both work best when the property is sized properly first, and both pair well with solar and a battery, since a heat pump running on your own generation costs considerably less than one running on imported electricity.