Air-to-air heat pumps: the UK homeowner's guide

An air-to-air heat pump is a split-system air conditioner that runs in reverse. An outdoor unit pulls heat out of the outside air (there is heat in it even at minus 15°C), a refrigerant carries it indoors through two slim pipes, and a wall-mounted indoor unit blows it into the room. Flip the mode in July and the same box takes heat out of the room instead. Every wall-mounted split we review is one of these, whatever the brochure calls it.

The reason it matters this winter is efficiency. A modern R32 unit has a seasonal coefficient of performance (SCOP) of about 4 to 5, which means each kilowatt-hour of electricity delivers four to five kilowatt-hours of heat. A fan heater, panel heater, storage heater, or infrared panel delivers exactly one. At Ofgem's July to September 2026 cap of 26.11p/kWh, that is 26p per unit of heat from a resistive heater against roughly 5p to 7p from an air-to-air heat pump. Around 1.7 million UK homes still heat with storage heaters, according to an Octopus Energy figure, and those homes have the most to gain.

The catches are real too. An air-to-air unit heats the room it is fitted in, not the radiators elsewhere, and it does not heat your hot water. The rest of this page sorts the homes it suits from the ones it does not. If you already know, compare local F-Gas registered installers and get quotes.

The cycle is the same one your fridge uses, pointed the other way. In heating mode:

1. The outdoor unit's fan draws outside air over a coil of cold refrigerant. Even in winter the air is warmer, so heat moves into the refrigerant and it boils into a gas.

2. A compressor squeezes that gas, raising its temperature well above room temperature.

3. The hot gas flows indoors to the wall unit, where a second coil and a quiet fan release the heat into the room.

4. Condensed back to a liquid, the refrigerant returns outside and the cycle repeats.

The compressor is inverter-driven, so it speeds up and slows down to hold the temperature you set rather than switching on and off. In summer a reversing valve swaps the roles of the two coils and the unit cools instead. For the longer version, read how air conditioning works and can air conditioning heat your home?.

Two things rule it out. First, an air-to-air system does not connect to radiators or a hot water cylinder. If you want one system to heat every room and your water, you are looking at an air-to-water heat pump, which attracts the larger £7,500 grant; our air-to-air vs air-to-water comparison walks through that decision.

Second, heat only goes where an indoor unit is. A single unit in the hallway will not warm three bedrooms with the doors shut, so whole-house air-to-air means a multi-split with a unit in most rooms, at £3,500 to £7,000 or more. Draughty houses with lots of small rooms are the hardest case: fix the insulation first, or let the heat pump carry the living areas and something else carry the rest.

The Boiler Upgrade Scheme has offered £2,500 towards an air-to-air heat pump since 28 April 2026, in England and Wales, for homes only. The conditions are strict: an MCS-certified installer fitting an MCS-certified product, replacing an existing fossil fuel or electric heating system, and sized to heat the whole property on its own. It is one grant per property, shown as a discount on the installer's quote, and separate from the £7,500 air-to-water grant. A unit fitted only to cool one bedroom will not qualify.

What the paperwork does not tell you is that, as of mid-September 2026, almost nobody has received it. MCS is still completing the scheme: installer certification bodies were not yet accredited when UKAS approved the scheme update on 11 September, and the first products on the MCS directory, listed on 1 September, were 65 Daikin multi-split combinations, with no single splits from any brand. ECIU counted around 45 voucher applications and no completed installations in July. Treat the grant as real, legal, and not yet claimable for most systems: get quotes with and without it, check the MCS directories yourself, and read our air-to-air heat pump grant guide before you commit.

In England, a reverse-cycle unit that heats as well as cools can be permitted development under Class G, as amended on 29 May 2025. A cooling-only unit cannot. The limits are 1.5m³ per outdoor unit, two units on a detached house or bungalow and one on a semi, terrace, or flat, and the unit must meet the MCS 020-a noise standard: 37 dB(A) one metre from a neighbour's nearest habitable-room window or door. Listed buildings, conservation areas, and flats where the wall belongs to the freeholder need separate consent, and the devolved nations have their own rules, so check with your local planning authority first.

A modern outdoor unit runs at around 45 to 50 dB(A) at one metre and the good ones drop below 40 in quiet mode, so siting is what makes or breaks the 37 dB(A) test. Indoors, the units above start at 19 dB(A). Our planning permission guide has the Class G wording in full and are air-to-air heat pumps noisy? explains the numbers.

Three habits make the difference. Set the temperature you want and leave it, because an inverter compressor sips power holding a room steady and gulps it catching up from cold. Point the louvres down, since warm air rises. And keep the outdoor unit clear of leaves and snow; in cold, damp weather it will pause for a few minutes now and then to defrost, which is normal.

Efficiency falls as the outside temperature drops, but the units above keep heating at minus 15°C to minus 20°C and still return a multiple of a panel heater's one-to-one. On a time-of-use tariff, running harder overnight on cheap electricity cuts bills further. Read heating with air conditioning, the most efficient way to run an air-to-air heat pump, do air-to-air heat pumps work in cold weather?, and heat pump electricity tariffs, and book a winter service if the unit has been cooling all summer.