Air Source Heat Pumps

What do air source heat pumps do?

Air source heat pumps allow you to heat a property using energy absorbed from the air. They do this by absorbing heat from the air outside the property, which is used to heat radiators, underfloor heating systems, warm air convectors and hot water.

What types of air source heat pumps are there?

Air source heat pump systems come in two main types

Air-to-water system
Distributes heat via a wet central heating system. Heat pumps work more efficiently at lower temperatures than standard boiler systems, and as such are more suited to underfloor heating systems or larger radiators, as these give out heat at lower temperatures over a longer timespan.

Air-to-air systemProduces warm air for circulation by fans. If you want to heat water as well, this is probably not the system for you.

How do air source heat pumps work?

Heat pumps work by absorbing heat from the air into a liquid and pumping it through a heat exchanger in the heat pump. The low-grade heat is extracted using a refrigeration system, in the same way that a fridge extracts heat from its inside, and pushed through the heat pump compressor. It is then concentrated into a higher temperature, capable of heating water for the heating or hot water circuits of a house. It is possible for air source heat pumps to extract heat from the air even with an outside temperature at minus 15° C.

As the heat pumps run on electricity, there is some impact on the environment, but the advantage is that heat they extract from the ground, air, or water is constantly and naturally renewed.

Unlike traditional boilers, fuelled by gas or oil, these ground pumps deliver heat at lower temperatures over much longer periods. This means that during colder spells they may need to be left on 24 hours, 7 days a week in order to heat a property efficiently. It also means that radiator surface temperatures should not be as high as they would when attached to a traditional system.

What are the benefits of air source heat pumps?

  • May be easier to install than a ground source heat pump, but efficiencies may also be lower
  • Reduced fuel bills, particularly in comparison to, for example, electrically-heated premises
  • Smaller carbon footprint. Heat pumps can have lower carbon emissions than the fuel used by many more conventional systems
  • No fuel purchases and deliveries needed
  • Able to provide both general heating and hot water
  • Reduced maintenance requirement

Is an air source heat pump suitable?

Here are a few key questions to consider:

Is there somewhere to put it?
It needs to be fitted to an outside wall or placed on the ground. There must be sufficient space for a good flow of air around the device. A wall that catches plenty of sun is the ideal situation.

Is the property well insulated? 
Air source heat pumps produce heat at a lower temperature than traditional boilers. For this type of system to be effective it is essential that the property should be well insulated and draught-proofed.

What fuel is currently being used?
An air source system will pay for itself in a much shorter time span if it is replacing an electric or coal heating system. (Heat pumps are not advised for homes served by the gas network.)

What type of heating system is planned? 
Air source heat pumps work better with underfloor or warm air heating than with radiator-based systems, which require higher water temperatures

Is the system intended for a new development?
The cost can be reduced by installing it in conjunction with other building works.

What are the Costs and Savings?

Typical system cost, say for a detached domestic property, will range from around £6,000 to £10,000 including installation.

The cost of running the system will depend upon a range of factors, including the size of the property and the level of insulation.

These will depend on several factors; some of them are set out below.

It is important that the system is appropriately controlled for the demands being placed upon it. Actual savings figures will always depend on relevant exact fuel prices

Heat distribution method:
According to our research many experts favour underfloor heating to provide a more efficient solution than radiators. As previously stated, this is because the water does not need to reach such a high temperature. Where underfloor heating is not an option, then radiators should be as large as possible. Advice can be sought from the installer.

Fuel costs:
Using an air source heat pump does not mean an end to fuel bills, because the pumps are powered by electricity. Any savings will be affected by the price of your previous fuel as well as the price of the electricity needed to run the devices.

Old and new system efficiency:
The efficiency of your old heating system will have dictated its running costs. The difference between running the heat pumps and an inefficient older system will be greater, giving bigger savings.

Hot water:
If the purpose of either the new or old system is supply hot water as well as heating, running costs will be higher. When preparing a comparison make sure they are like for like.

Temperature setting:
If you use the heat pumps to increase the ambient temperature of your building from previous levels with your old heating system then you can expect your heating bills to be higher and no savings to be made. 18 to 21 degrees Celsius is the optimum setting for your thermostat.

Using the controls:
Efficient and effective control of the system is the only way to get the most out of it. Ask your chosen installer to explain in detail how to control the system for maximum efficiency.

Want to know more?

To find renewable technologies to suit your property, try the Energy Saving Trust energy selector tool at.

Curious about the Technologies?

For more information on home energy generation technologies, contact your local Energy Saving Trust Advice Centre on 0800 512 012.

For specific technology questions, visit the Heat Pump Association at