Air source heat pumps
Heat your home with energy absorbed from the air around you.
Air source heat pumps absorb heat from the outside air. This heat can then be used to heat radiators, underfloor heating systems, or warm air convectors and hot water in your home.
An air source heat pump extracts heat from the outside air in the same way that a fridge extracts heat from its inside. It can get heat from the air even when the temperature is as low as -15° C. Heat pumps have some impact on the environment as they need electricity to run, but the heat they extract from the ground, air, or water is constantly being renewed naturally.
Air source heat pumps (also known as ASHPs):
- could lower your fuel bills, especially if you are replacing conventional electric heating
- could provide you with an income through the government’s Renewable Heat Incentive (RHI)
- could lower your home’s carbon emissions, depending on which fuel you are replacing
- don't need fuel deliveries
- can heat your home and provide and hot water
- need little maintenance - they're called ‘fit and forget’ technology
- can be easier to install than a ground source heat pump, though efficiencies may be lower.
Unlike gas and oil boilers, heat pumps deliver heat at lower temperatures over much longer periods. During the winter they may need to be on constantly to heat your home efficiently. You will also notice that radiators won't feel as hot to the touch as they might do when you are using a gas or oil boiler.
Heat from the air is absorbed at low temperature into a fluid. This fluid then passes through a compressor where its temperature is increased, and transfers its higher temperature heat to the heating and hot water circuits of the house. There are two main types of air source heat pump system:
- An air-to-water system distributes heat via your wet central heating system. Heat pumps work much more efficiently at a lower temperature than a standard boiler system would. So they are more suitable for underfloor heating systems or larger radiators, which give out heat at lower temperatures over longer periods of time.
- An air-to-air system produces warm air which is circulated by fans to heat your home. They are unlikely to provide you with hot water as well.
To tell if an air source heat pump is right for you, there are a few key questions to consider:
- Do you have somewhere to put it? You'll need a place outside your home where a unit can be fitted to a wall or placed on the ground. It will need plenty of space around it to get a good flow of air. A sunny wall is ideal.
- Is your home well insulated? Since air source heat pumps work best when producing heat at a lower temperature than traditional boilers, it's essential that your home is insulated and draught-proofed well for the heating system to be effective.
- What fuel will you be replacing? The system will pay for itself much more quickly if it's replacing an electricity or coal heating system. Heat pumps may not be the best option for homes using mains gas.
- What type of heating system will you use? Air source heat pumps can perform better with underfloor heating systems or warm air heating than with radiator-based systems because of the lower water temperatures required.
- Is the system intended for a new development? Combining the installation with other building work can reduce the cost of installing the system.
You may also want to consider ground source heat pumps, which use pipes buried in the garden to extract heat from the ground. Or use our Renewable Selector to find out which means of generating energy might work best for you.
Installing a typical system costs around £6,000 to £10,000. Running costs will vary depending on a number of factors - including the size of your home, and how well insulated it is, and what room temperatures you are aiming to achieve.
How much you can save will depend on what system you use now, as well as what you are replacing it with. Your savings will be affected by:
Your heat distribution system
If you have the opportunity, underfloor heating can be more efficient than radiators because the water doesn’t need to be so hot. If underfloor heating isn’t possible, use the largest radiators you can. Your installer should be able to advise on this.
Your fuel costs
You will still have to pay fuel bills with a heat pump because it is powered by electricity, but you will save on the fuel you are replacing. If the fuel you are replacing is expensive you are more likely to make a saving.
Your old heating system
If your old heating system was inefficient, you are more likely to see lower running costs with a new heat pump.
If the heat pump is providing hot water then this could limit the overall efficiency. You might want to consider solar water heating to provide hot water in the summer and help keep your heat pump efficiency up.
Using the controls
Learn how to control the system so you can get the most out of it. You will probably need to set the heating to come on for longer hours, but you might be able to set the thermostat lower and still feel comfortable. Your installer should explain to you how to control the system so you can use it most effectively.
These are the savings you might make every year when replacing an existing heating system in an average three-bedroom semi-detached home with a typical ASHP installation and a good installation:
Air source heat pump performing at 220%
Air source heat pump performing at 300%
A negative number means it could cost you more to run the heat pump than the system you are replacing. We've assumed average boiler efficiency for each fuel type; heat pumps produce more energy (as heat) than they use (as electricity), so their efficiency is more than 100%. Find out more about how we made these calculations.
You may be able to receive payments for the heat you generate using a heat pump through the government’s Renewable Heat Incentive (RHI). This scheme should be launched in Summer 2013.
For systems installed after 1 August 2011, you may be able to get help with the installation costs of a new air source heat pump through the Renewable Heat Premium Payment scheme.
Green Deal finance and renewables
This technology is an eligible measure under the UK government’s Green Deal which is a financing mechanism that lets people pay for energy-efficiency improvements through savings on their energy bills.
Further information on Green Deal.
Heat pump systems typically come with a 10 year warranty. You can expect them to operate for 20 years or more, however they do require regular scheduled maintenance. A yearly check by you and a more detailed check by a professional installer every 3-5 years should be sufficient. The installer should leave written details of any maintenance checks you should undertake to ensure everything is working properly. Consult with your supplier for exact maintenance requirements before you commit to installing a heat pump.
One of the yearly checks that you are likely to be advised to carry out is to check that the air inlet grill and evaporator are free of leaves or other debris. Any plants that have started to grow near the heat pump unit will also need to be removed. You may also be advised by your installer to check the central heating pressure gauge in your house from time to time. If so, you should be shown how to do this.
To prevent the heat pump from freezing in cold winter weather anti-freeze is used. Levels of anti-freeze and its concentration is one of the things that a professional installer will check when he comes to service your heat pump.
If your heat pump has external refrigeration pipes (very unusual for a domestic system) these will need to be serviced annually by a refrigeration engineer.
Air source heat pump installations In Wales and Northern Ireland require planning permission. In England and Scotland they may be considered Permitted Development, in which case you will not need planning permission, but the criteria are complex so it is always a good idea to check with your local planning office.
From 1st December 2011, domestic air source heat pump systems will be classed as Permitted Development provided that they comply with certain criteria, including:
- there is no wind turbine at the property
- the external unit is less than 0.6 m3 in size
- the unit is more than one metre from the edge of the householder's property
- it is not on a pitched roof, or near the edge of a flat roof
- it meets additional criteria if in a conservation area, World Heritage Site or similar.
This list is not comprehensive. Read the full legislation at the government's legislation website or contact your local planning office for full details.
A domestic installation of an air source heat pump in Scotland is currently permitted unless:
- it would result in the presence within the curtilage of a dwelling of more than one air source heat pump
- the air source heat pump would be situated less than 100 metres from the curtilage of another dwelling
- the air source heat pump is visible from the road in a conservation area
- the air source heat pump would be within a World Heritage Site or the curtilage of a listed building
In addition, before beginning the development the developer must apply to the planning authority for:
- a determination as to whether the prior approval of the authority will be required for the siting and external appearance of the air source heat pump
- the application also needs to be accompanied by a range of other information and a number of other conditions apply. Read the relevant Scottish legislation for details (PDF, 50K).