Heating & cooling guide
Air-to-air heat pumps: heating and cooling for UK homes (2026)
Last updated 2026-11-02
An air-to-air heat pump is the only home heating system that also cools, which is why it is suddenly interesting to UK homeowners. But it is also the one heat pump type the government grant deliberately excludes. This guide explains what an air-to-air system actually does, what it costs in 2026, and the specific circumstances where it beats a conventional air-to-water heat pump.
The short version: air-to-air is excellent for one or two rooms, for flats without radiators, and for anyone who wants air conditioning in summer. It is a poor fit for a whole house that needs hot water, and you get no £7,500 Boiler Upgrade Scheme grant.
What is an air-to-air heat pump?
An air-to-air heat pump moves heat from the outside air into your rooms using a refrigerant circuit instead of water. An outdoor compressor unit connects by refrigerant pipework to one or more indoor units, which blow warmed air into the room. In summer a reversing valve changes the direction of flow and the same hardware becomes an air conditioner.
Physically, an air-to-air heat pump and a split-system air conditioner are the same product. The distinction is mostly marketing and installation intent: sold for year-round heating and cooling it is called a heat pump, sold mainly for summer comfort it is called air conditioning. Either way it is a reverse-cycle system with a coefficient of performance (COP) of roughly 3 to 4 in mild conditions.
The key limitation is not efficiency, it is delivery. Air carries far less heat per cubic metre than water, so air-to-air cannot practically supply a hot water cylinder or feed existing radiators.
Air-to-air vs air-to-water: the key difference
This is the single most important decision, and it comes down to what you need to heat.
| Feature | Air-to-air | Air-to-water |
|---|---|---|
| Heats radiators / underfloor | No | Yes |
| Heats hot water | No | Yes |
| Cools in summer | Yes | Rarely (some fan coils) |
| £7,500 BUS grant | Not eligible | Eligible |
| Typical installed cost | £1,500–£7,000 | £9,000–£14,000 |
| Net cost after grant | £1,500–£7,000 | £1,500–£6,500 |
| Comfort type | Warm air, fast response | Radiant, slow response |
| Best for | Rooms, flats, open plan, cooling | Whole house with wet system |
For a broader comparison of every wet heating alternative, see air source heat pump vs gas boiler.
Can an air-to-air heat pump heat a whole house?
Technically yes, in practice rarely on its own. A whole-house air-to-air installation means a multi-split system with an indoor head in every main room, typically three to five heads on one or two outdoor units. That is achievable and common in Scandinavia and southern Europe.
Three practical obstacles make it awkward in most UK homes:
- Hot water. It cannot heat a cylinder, so you need a separate immersion heater, a dedicated hot water heat pump, or a retained boiler. That second system adds cost and complexity.
- Room-by-room zoning. Warm air heats the room it is blown into. Hallways, landings and bathrooms are hard to serve, and doors need to stay open for heat to migrate.
- Comfort expectations. UK homes are designed around radiators and radiant heat. Warm air feels different: quicker to respond, but with more air movement and a drier feel.
Where whole-house air-to-air works well is in well-insulated open-plan spaces, new builds with mechanical ventilation, and flats where there is no radiator circuit at all. For a room-by-room view of what a wet system needs, see do you need to replace your radiators for a heat pump.
What does an air-to-air heat pump cost in the UK?
Indicative 2026 installed prices, including a standard bracket and short pipe run:
- Single split (one room): £1,500–£3,000, a 2.5–3.5 kW indoor unit on one outdoor unit
- Multi-split (two rooms): £2,500–£4,500
- Multi-split (three to four rooms): £3,500–£7,000
- Add a hot water heat pump instead of a boiler: £2,500–£4,000 extra
Long pipe runs, condensate drainage to a distant drain, listed building constraints and outdoor units mounted at height all push these numbers up. Because air-to-air is not grant funded, there is no £7,500 offset, you pay the full figure. Compare that with the net cost of a grant-assisted wet system in our heat pump cost guide.
Why air-to-air heat pumps miss the £7,500 grant
The Boiler Upgrade Scheme funds a specific technology list: air source heat pumps that supply wet heating and hot water, ground source heat pumps, and water source heat pumps. Air-to-air systems are excluded because they cannot deliver domestic hot water, and because the scheme is designed to replace fossil-fuel boilers and their associated wet systems.
The effect on value is bigger than it first appears. A £12,000 air-to-water install becomes roughly £4,500 after the grant. A £5,000 multi-split air-to-air install stays at £5,000. So the grant narrows the price gap far more than the headline prices suggest, which is why the cheaper option frequently is not.
If your circumstances are low income or you receive qualifying benefits, the ECO4 scheme can fund a wet heat pump at no cost at all. Air-to-air is not covered there either.
Running costs and efficiency compared
Air-to-air and air-to-water heat pumps have similar efficiency ranges: both typically achieve a seasonal COP of 2.8 to 4.0 depending on climate, insulation and how well the system is commissioned. Air-to-air often has a slight edge in mild weather and a disadvantage in very cold weather, when warm-air delivery at high output feels cooler.
The real running-cost difference comes from what else you are powering. An air-to-air home typically still runs a boiler or immersion for hot water, and may keep gas standing charges. Removing gas entirely is where the meaningful savings sit. Our guide to heat pump running costs breaks down the numbers, and heat pump tariffs covers the off-peak rates that improve the economics most.
Where an air-to-air heat pump makes sense
Good fit:
- A flat or maisonette with no gas supply and no radiator circuit
- One or two rooms that are hard to heat with the existing system, such as a converted loft, an extension or a garden office
- Anyone who genuinely wants summer cooling, which no wet heat pump provides
- Commercial spaces, where air-to-air is the standard answer and grant rules differ
Poor fit:
- A whole house that needs hot water and already has radiators, where an air-to-water system with the grant wins on total cost
- Period properties with solid walls and high heat loss, where air-to-water with upsized radiators is the better route
- Anyone relying on grant funding to make the project affordable
If you are weighing up several routes at once, our alternatives to gas boilers comparison puts air-to-air alongside hybrids, electric boilers, infrared and biomass.
Do you need planning permission?
In England, domestic air source heat pumps, including air-to-air, normally fall under permitted development if the outdoor unit meets the noise limit of 42 dB at the nearest neighbour assessment position, sits within permitted boundaries, and the building is not a flat or listed. Scotland, Wales and Northern Ireland have their own rules, and conservation areas can restrict where a unit is sited.
Full detail, including the MCS 020 noise assessment, is in our guide to heat pump planning permission.
Frequently asked questions
What is an air-to-air heat pump?
An air-to-air heat pump moves heat between the outside air and the air inside your rooms, using a refrigerant circuit rather than water. In winter it extracts heat from outdoor air and blows warmed air into the room; in summer the reversing valve flips and it works as an air conditioner. It is the same technology as a split-system air conditioner, which is why the two terms are often used interchangeably.
Is an air-to-air heat pump eligible for the £7,500 Boiler Upgrade Scheme grant?
No. The Boiler Upgrade Scheme only funds air-to-water heat pumps (the type that heat radiators and hot water) and ground source or water source heat pumps. Air-to-air systems distribute heat as warm air and cannot supply domestic hot water, so they are excluded from the grant. You pay the full installation cost.
Can an air-to-air heat pump heat a whole house in the UK?
It can, but only with a multi-split or multi-head system with a unit in every main room, and typically not the bathrooms. Warm air heating suits open-plan and well-insulated spaces. It does not heat hot water, so you still need an immersion heater, cylinder or combi boiler for showers. For most UK homes with existing radiators and a hot water cylinder, an air-to-water heat pump is a better whole-house fit.
How much does an air-to-air heat pump cost in the UK?
A single-room split system typically costs £1,500–£3,000 installed. A multi-split system covering three to four rooms usually runs £3,500–£7,000 depending on pipe runs and unit quality. Because air-to-air is not grant funded, that is the full price you pay, compared with roughly £2,500–£6,500 net for a grant-assisted air-to-water system.
Do air-to-air heat pumps need planning permission?
In England, domestic air source heat pumps usually fall under permitted development provided the outdoor unit meets the noise limit of 42 dB at the nearest neighbour assessment position, sits within permitted boundaries, and the property is not a flat or listed building. Rules differ in Scotland, Wales and Northern Ireland, and conservation areas can restrict siting. Always confirm with your local planning authority before installing.
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