Air-to-air heat pumps
An air-to-air heat pump delivers warm air straight into a room. It does not heat water, which means it does not serve radiators and does not supply hot taps — a genuinely different product from the air source heat pumps most people have read about.
Read this first
An air-to-air heat pump does not heat water. It cannot feed radiators and it cannot supply hot water to your taps. If you want a single system that replaces a boiler for both heating and hot water, you are looking for an air-to-water system instead.
What air-to-air means
The heat pump takes heat from outdoor air, as any air source system does. The difference is what it does with it. Rather than transferring the heat into water, it transfers it into air and blows that air directly into the room through an indoor unit mounted on a wall or ceiling.
There is no water circuit, no radiators and no cylinder. Each room or space you want heated has its own indoor unit, fed by refrigerant pipework from a single outdoor unit.
How it differs from an air-to-water heat pump
The outdoor unit looks much the same either way. What differs is what happens to the heat once it is inside, and that is what decides whether the system can do what you need.
Air-to-air
Heat goes straight into the room as warm air, through an indoor unit on the wall. There is no water circuit — so no radiators, and no hot water for your taps. Every room you want heated needs its own indoor unit.
Air-to-water
Heat goes into water, which circulates through radiators or underfloor heating and fills a cylinder for the taps. It does the same jobs a boiler did, which is why it is the type most UK homes install. See air source heat pumps.
| Air-to-air | Air-to-water | |
|---|---|---|
| What it heats | Air, delivered into rooms | Water, for radiators and a cylinder |
| Hot water for taps | No — a separate system is needed | Yes, via a hot water cylinder |
| Works with radiators | No | Yes |
| Indoor equipment | A wall or ceiling unit in each room served | Heat pump unit and cylinder |
| Cooling in summer | Commonly available on the same unit | Only where designed in, and uncommon |
| Grant value | £2,500, residential only | £7,500 |
The industry frequently uses "air source heat pump" to mean the air-to-water type, which is why the two get confused. Both are air source. Only one of them will run your radiators.
Heating and cooling
Because the system moves heat through refrigerant and delivers it as air, many units can run in reverse and cool the room in summer. That is a real advantage over a wet system, where cooling is unusual and has to be designed in from the start.
It is also the reason these units are often sold as air conditioning. The same box, used in the other direction, is a heater — and a far more efficient one than an electric radiator, because it is moving heat rather than making it.
Where it suits a home
Air-to-air makes most sense where there is no wet central heating system to work with, or where the heating problem is confined to particular spaces:
- properties heated by electric panel heaters or storage heaters, with no radiator circuit;
- extensions, loft conversions, garden rooms and home offices;
- flats and small properties where a cylinder cannot be accommodated;
- spaces where summer cooling is as much of a priority as winter heating.
It suits a home less well where there is an existing wet system in good order, or where hot water is part of the problem you are trying to solve. In those cases you would be adding a second system rather than replacing one.
What to plan for
- Hot water. Decide how it will be provided before anything else. This is the question that most often changes the answer.
- Visible indoor units. One per space served, in a position that suits the airflow rather than the décor. Some people mind this; it is worth knowing in advance.
- The outdoor unit. Same considerations as any air source system — clear airflow, sensible siting, room to service it.
- Air movement. These systems heat by blowing warm air, which feels different from radiators. Unit position affects comfort noticeably.
Grant support
In England and Wales, an eligible air-to-air heat pump installation currently attracts £2,500 under the Boiler Upgrade Scheme. Two limits are worth stating plainly: the value is lower than for air-to-water and ground source systems, and air-to-air is eligible in residential properties only — it is not eligible in non-residential buildings.
Everything else about the scheme applies as normal: the property has to meet the general criteria, the existing heating system has to be fully replaced, and an MCS-certified installer makes the application on the property owner's behalf. The values are set out on our heat pump grants page, and the criteria on the eligibility page.
Related
Air source heat pumps
The air-to-water type: radiators, underfloor heating and hot water from one system.
Heat pumps explained
All three types side by side, and what each asks of a property.
Heat pump grants
Every current value, including the residential-only air-to-air figure.
Check eligibility
The main criteria, and a short check for your property.
Is my home suitable for a heat pump?
Which properties are straightforward, and which need more planning.
Boilers
If a wet heating system is staying, what your boiler options are.
Frequently asked questions
- Is an air-to-air heat pump the same as air conditioning?
- The hardware is closely related. An air conditioner moves heat out of a building; an air-to-air heat pump can run in both directions, so it heats in winter as well as cooling in summer. Many units on the market do both.
- Can it heat my hot water?
- No. It heats air, not water. Hot water for taps and showers has to come from something else — an immersion, a separate hot water heat pump or an existing system. This is the most important thing to understand before choosing one.
- Can I use it with my existing radiators?
- No. Radiators need hot water circulating through them, and an air-to-air system does not produce any. If you want to keep a wet heating system, you need an air-to-water system instead.
- How many indoor units would I need?
- One in each room or open space you want heated. That is a practical difference from a wet system, where the heat is distributed by pipework you already have — here, every room served needs its own visible unit.
- Is it eligible for a Boiler Upgrade Scheme grant?
- Yes, at £2,500, in residential properties only. It is not eligible in non-residential buildings, and the rest of the scheme criteria still apply.
- Would it suit a whole house?
- It can, but you would need units in each space and a separate solution for hot water. Air-to-air tends to make most sense in properties without a wet heating system, in extensions and garden rooms, or where a small number of spaces need heating and cooling.