Air to Air Heat Pumps Explained How They Work, How They Compare to Air to Water, and Who They Suit
Air to air heat pumps are one of the quickest ways to cut down on gas heating, and you may already know them by another name. They are the same systems people call air conditioning, used to heat as well as cool. Here is how they work, how they compare to other heat pumps, and whether one suits your home.
An air to air heat pump moves heat from the outside air into your home and blows it into the room as warm air through indoor units. It is the same technology as split air conditioning, so it can cool in summer too. Unlike air to water heat pumps, it does not heat radiators or hot water, which makes it quicker to install and ideal for heating and cooling the rooms you use most.
What Is an Air to Air Heat Pump?
An air to air heat pump takes heat from the outside air and moves it indoors, where it is blown into the room as warm air. It does this with a refrigerant circuit, an outdoor unit and one or more indoor units, so the heat is moved rather than made by burning fuel. That is why heat pumps can deliver more heat energy than the electricity they use to run.
If that sounds like air conditioning, that is because it is. A modern split air conditioner is an air to air heat pump. In summer it runs in reverse and moves heat out of the room. The term "air to air heat pump" is simply used when the focus is on heating rather than cooling.
How It Works, Step by Step
- The outdoor unit collects heat. A fan draws outside air across a coil filled with cold refrigerant. Even on a cold day there is heat in that air, and the refrigerant absorbs it.
- The compressor raises the temperature. Compressing the refrigerant pushes its temperature up, a bit like a bicycle pump getting warm as you use it.
- The indoor unit releases the heat. The hot refrigerant travels through insulated pipes to the indoor unit, where a fan blows room air across the warm coil and back into the room.
- The cycle repeats. The refrigerant returns outside, cools down and picks up more heat. The system adjusts its speed to hold the temperature you have set.
Air to Air vs Air to Water Heat Pumps
Most heat pump talk in the UK is about air to water systems, which replace a boiler and feed radiators or underfloor heating. Air to air works differently, and the right choice depends on the home.
| Air to Air | Air to Water | |
|---|---|---|
| How heat is delivered | Warm air from wall, floor, ceiling or ducted indoor units | Hot water to radiators or underfloor heating |
| Hot water | No, a separate hot water system is needed | Yes, usually with a hot water cylinder |
| Cooling | Yes, the same units cool in summer | Not normally |
| Changes to the home | Indoor units and pipe runs, no radiator changes | Often larger radiators, a cylinder and new pipework |
| Heat-up speed | Fast, rooms warm up within minutes | Slower, designed to run low and steady |
| Room control | Each indoor unit set separately | Usually whole-house or zone control |
For many homes the best fit is air to air in the rooms that are used most, such as the living room, bedrooms and a home office, alongside the existing system for hot water. For a full boiler replacement, an air to water system may be the better route. Our renewable solutions page covers both.
How Efficient Are Air to Air Heat Pumps?
Efficiency is measured by how much heat the system delivers for each unit of electricity it uses. Over a whole heating season this is shown as SCOP, the seasonal coefficient of performance, and on the energy label as a heating rating. A good modern unit will deliver several times more heat than the electricity it uses over a typical winter.
Real-world efficiency depends on a few things:
- Correct sizing. A unit that is too small runs flat out and struggles, while one that is far too big wastes energy cycling on and off. Our sizing guide explains how it is worked out.
- Insulation. Heat pumps work best in homes that hold their heat. Good loft insulation and draught-proofing make a noticeable difference.
- Outdoor temperature. Efficiency drops as it gets colder outside, but quality units keep heating well below freezing. Panasonic rates its current Etherea range to heat at outdoor temperatures down to -20°C.
- Servicing. Clean filters and a healthy refrigerant circuit keep the system working as designed. See our air conditioning servicing page.
The Pros and Cons
Strengths
- Heating in winter and cooling in summer from one system
- Rooms warm up quickly
- Each room can be set to its own temperature
- No changes to radiators or pipework
- Wi-Fi and app control on most current models
- Filters on many models help clean the air
Things to Consider
- Does not heat your hot water
- Indoor units are visible unless you choose ducted
- Needs a suitable spot for the outdoor unit
- Warm air feels different from a radiator
- Works best in well-insulated rooms
Is There a Grant for Air to Air Heat Pumps?
Air to air heat pumps have been added to the government Boiler Upgrade Scheme rules in England and Wales. To qualify, the system has to replace the home's main heating, any fossil fuel boiler has to be removed, and the installer has to be certified under the Microgeneration Certification Scheme (MCS) for air to air systems.
Which Homes Suit an Air to Air Heat Pump?
- Homes that get too hot in summer. If you want cooling anyway, air to air gives you efficient heating for no extra equipment.
- Rooms the central heating struggles with. Extensions, loft conversions, conservatories and garden rooms are common examples.
- Flats and homes without gas. Air to air is a strong option where electric panel heaters or storage heaters are the current heating.
- Home offices. Heating or cooling one room during the day, without running the whole house, is where air to air really earns its keep.
- Homes with an oil or LPG boiler. Air to air in the main living spaces can take a big share of the heating load.
For a closer look at using air conditioning as your main heating, read can air conditioning heat your home.
Common Questions
Is an air to air heat pump the same as air conditioning?
Yes. A split air conditioner with a heating mode is an air to air heat pump. The name used usually depends on whether the focus is heating or cooling.
Can an air to air heat pump heat a whole house?
It can, with an indoor unit in each main room or a ducted system serving several rooms. You would still need a separate way to heat your hot water, which is why many homes use air to air for the rooms and keep their existing system for hot water.
Do air to air heat pumps work in winter?
Yes. They are designed to keep heating in cold weather, and good units keep working well below freezing. On very cold, damp days the outdoor unit will briefly defrost itself, which is normal.
Are air to air heat pumps noisy?
Indoor units are very quiet in normal use, and the outdoor unit makes a low hum when it is working hard. Siting the outdoor unit carefully keeps noise away from bedrooms and neighbours.
Do I need planning permission?
In England, a single outdoor unit is usually covered by permitted development rights as long as it meets certain size and position limits. Listed buildings and conservation areas can be different, and we check this at survey.
How long does installation take?
A single room is usually fitted in a day. Multi-room and ducted systems take longer, and we give you a clear timeline before any work starts.
Get a Free Survey
Our F-Gas certified engineers will look at your rooms, insulation and outdoor space, then recommend the right air to air system for your home, whether that is one unit for a cold extension or heating and cooling for the whole house. We're a Panasonic Pro Partner and Mitsubishi Electric installer, covering London, Kent, Essex, Sussex and the South East. Call us on 01322 474 990.
Find out more about our air conditioning service.