Air Source Heat Pumps (ASHPs)

air source heat pumpAir source heat pumps absorb heat from the outside air and use this to heat radiators, underfloor heating systems, or warm air convectors and hot water in your home. An air source heat pump works like a fridge in reverse  to extract heat from the outside air and use it inside your home. They can get heat from cold air (in fact as low as -15° C).

Due to their low temperature output and efficiency range, air force heat pumps are better matched to underfloor heating than to radiators in the home.

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.

The benefits of Air Source Heat Pumps

Air source heat pumps can heat your home and provide hot water and:

  • could lower your fuel bills (heat pumps are run by electricity)
  • could provide you with an income through the government’s Renewable Heat Incentive (RHI)
  • could lower your home’s carbon emissions (heat pumps need electricity to run so they have some impact on the environment, the heat they extract from theair is renewed naturally)

Heat pumps deliver heat at lower temperatures so they need to be working over longer periods than boilers, during the colder weather they may need to be running constantly. If heating radiators you will notice they are not as hot as when heated by a boiler. 

Air source heat pumps can be easier to install than a ground source heat pump, though efficiencies may be lower.

How do ASHPs work?

Natural heat from the air is absorbed into a fluid within a pump unit mounted outside your home. This fluid then passes through a compressor causing the temperature to rise and transfers its 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.

Is an Air Source Heat Pump suitable for me?

Do you have somewhere to put it?

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, your home needs to be well insulated and draught-proofed for the heating system to be effective.

Best if replacing electric or coal heating

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 are best suited to being matched 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.

If you want an accredited ASHP installer to assess your home and help you choose the best setup to meet your needs call Steven Banks on 01462 636376

What are the typical costs, savings and earnings of ASHPs?


Installing a typical system costs between £6,000 to £10,000.

Running costs will depend on the size of your home, 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 home heating system – Underfloor heating is 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 fuel costs – Heat pumps use electricity to run, but you will save on the fuel you were using to heat your home/water. The more expensive the fuel you are replacing the 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.
  • Water heating – If your old heating system was inefficient, you are more likely to see lower running costs with a new heat pump
  • Using the controls effectively – 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.

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:

Existing system


Air source heat pump 
performing at 220%

Air source heat pump 
performing at 300%



Carbon dioxide/year







Carbon dioxide/year







Carbon dioxide/year







Carbon dioxide/year





A negative number means it could cost you more to run the heat pump than the system you are replacing. Assumes 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%. Source – Energy Saving Trust


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.

What maintenance is required for Air Source Heat Pumps?

Typically ASHPs come with a 10 year warranty and are expected to operate for 20 years or more, however they do require regular scheduled maintenance. They will require an annual check by you and a more detailed check by a professional installer every 3-5 years.

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  to check the central heating pressure gauge in your house from time to time.

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.

Do I need planning permission for ASHPs?

In England domestic air source heat pump systems are 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 etc.

This list is not comprehensive. Read the full legislation at the government’s legislation website or contact your local planning office for full details.

If you want an accredited ASHP installer to assess your home and help you choose the best setup to meet your needs call Steven Banks on 01462 636376