Air Source Heat Pumps (ASHPs)

Air Source Heat Pumps utilise heat from the outside air. The heat is then used to produce hot water or to heat you home. An Air Source Heat Pump works in the same way as a refrigerator. However, instead of removing heat from the air inside and transferring it outside, it removes heat from the air outside and transfers it inside.

It can get heat from the air even when the temperature is as low as -15° C because there is thermal energy in the air right down to −273.15° Celsius (−459.67° Fahrenheit.) Most people don’t realise this as they think there is no heat below 0° Celsius (-32° Fahrenheit) just because water freezes at this temperature.

Skip to section:
The advantages of an Air Source Heat Pump (ASHP)
How an Air Source Heat Pump (ASHP) works
Cost, savings and earnings

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The advantages of an Air Source Heat Pump (ASHP)

An Air Source Heat Pump (ASHP):

  • could reduce your fuel bills, especially if you are currently using oil or LPG
  • could generate you an income through the government’s Renewable Heat Incentive (RHI)
  • could reduce your home’s carbon footprint
  • will mean that you won’t need fuel delivered to your home
  • can produce heat and hot water for your home
  • needs little maintenance
  • is easier to install than a ground source heat pump

How an Air Source Heat Pump (ASHP) works

Heat from the outside air is absorbed into a liquid. The liquid then passes through a compressor where its temperature is raised because it is compressed, and transfers the heat to the central heating and hot water system in the home. There are two types of Air Source Heat Pump (ASHP):

  • An Air-to-Water Heat Pump system powers your central heating system and provides you with hot water.
  • An Air-to-Air Heat Pump System produces warm air which is circulated by fans to heat your home. It does not provide you with hot water.

Cost, savings and earnings

Typical Costs

Installation of an Air Source Heat Pump (ASHP) system will cost you between £8,000 to £15,000. The cost of running the Air Source Heat Pump (ASHP) system will depend on a number of criteria – including the size of the property to be heated, how well insulated the building is, and what temperature you require your home to be heated to.

Typical Savings

How much money you can save will be dependant on how you presently heat your home. The savings you will make will be determined by:

  • How you currently heat your home
    Underfloor heating is generally more efficient than a radiator system as the water doesn’t need to be as hot to produce the same indoor temperature. However, installing larger radiators can also have the same effect as you won’t need to concentrate high levels of heat into a small space to heat a room.
  • How much you are currently spending on fuel
    If you are spending a lot on fuel at the moment then you are likely to save more after installing an Air Source Heat Pump (ASHP).
  • How old your existing heating system is
    The older your existing heating system is the more inefficient it will be.
  • How much thought you put into managing your new Air Source Heat Pump (ASHP) heating system
    Learn how to manage the system efficiently to get the most out of it.

Below are examples of the savings that could be made each year when an existing heating system is replaced with an Air Source Heat Pump (ASHP) installation in a four bedroomed detached property:

Existing system  Savings per year RHI income per year
Gas older (non-condensing) £/year £250 to £450 £805 to £1,280
Carbon dioxide/year 1.2 to 2.5 tonnes
Electric (old storage heaters) £/year £500 to £1,100 £805 to £1,280
Carbon dioxide/year 5.5 to 11.0 tonnes
Oil older (non-condensing) £/year £500 to £900 £805 to £1,280
Carbon dioxide/year 2.2 to 3.8 tonnes
LPG older (non-condensing) £/year £1,175 to £1,860 £805 to £1,280
Carbon dioxide/year 2.0 to 3.5 tonnes
Coal £/year £450 to £850 £805 to £1,280
Carbon dioxide/year 6.0 to 10.75 tonnes

We’ve assumed different boiler efficiencies for each fuel type; heat pumps produce more energy (as heat) than they use (as electricity), so their efficiency is more than 100%.


You may be eligible to receive payments for all the heat you generate with an Air Source Heat Pump (ASHP) through the  Renewable Heat Incentive (RHI). For Air Source Heat Pump (ASHP) systems installed after the 1st of August 2011, you may also qualify for financial help with the installation costs of a new Air Source Heat Pump (ASHP) through the Renewable Heat Premium Payment scheme.

Green Deal

Air Source Heat Pumps (ASHPs) are eligible under the UK’s Green Deal which allows homeowners to pay for energy efficiency improvements through the savings they make on their energy bills. Read more about the Green Deal.