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Home & garden.

28 June 2021

Air source heat pumps explained

Find out how air source heat pumps work, how much they cost, and how much they could save you on your energy bills.
Sarah Ingrams
Air source heat pump

An air source pump is an alternative way to heat your home. It will enable you to generate your own renewable heat and potentially save money on your energy bills.

They deliver heat at lower temperatures than gas and oil boilers. So you'll need to run them for much longer periods to heat your home to a comfortable temperature. 

Heat pumps can save you more on your heating bills if you're replacing an expensive system such as electric storage heaters, oil, LPG (liquefied petroleum gas) or coal, rather than gas. But remember, a well-insulated home is essential – otherwise the heat the pump is generating escapes more easily.

Other options to generate your own heat include:

Read on to find out more about the pros and cons of air source heat pumps, so you can decide whether getting one is the right decision for you.

Make sure you're not paying too much for gas and electricity. Our independent switching site, Which? Switch, will help you to find a cheap energy deal.

Two air source heat pumps at the back of a home

How does an air source heat pump work?

An air source heat pump takes heat from the air and boosts it to a higher temperature using a compressor. It then transfers the heat to the heating system in your home.

They work a bit like refrigerators in reverse. 

  1. The air source heat pump absorbs heat from the outside air into a liquid refrigerant at a low temperature.
  2. Using electricity, the pump compresses the liquid to increase its temperature. It then condenses back into a liquid to release its stored heat.
  3. Heat is sent to your radiators or underfloor heating. The remainder can be stored in your hot water cylinder.
  4. You can use your stored hot water for showers, baths and taps.

The pump uses electricity to run, but it should use less electrical energy than the heat it produces. This makes them an energy-efficient way to warm your home.

Air source heat pumps work even if the temperature is well below zero.

Ground source heat pumps also harness natural heat and increase the temperature to warm your home. Find out how ground source heat pumps work.

Air source heat pump next to a blue wall

What is an air source heat pump? 

An air source heat pump is a low-carbon way of heating your home. They absorb heat from a cooler place and use it to increase the temperature inside your home. 

Air source heat pumps look similar to air-conditioning units. Their size depends on how much heat they'll need to generate for your home - the more heat, the bigger the heat pump.

There are two main types of air source heat pumps: air-to-water and air-to-air. They work in different ways and are compatible with different types of heating systems. 

Air-to-water heat pumps

Air-to-water heat pumps take heat from the outside air and feed it into your wet central heating system. 

They're most suitable for larger radiators or water underfloor heating because the heat they produce is cooler than that from a conventional gas or oil boiler. To be most effective they need a large surface area to release the heat.

It is more straightforward to incorporate larger radiators or underfloor heating for a heat pump while you're extending your home or in a new-build property. It can also cost less than retrofitting underfloor heating later on. 

Air-to-water heat pumps qualify for the Renewable Heat Incentive - a government scheme which could pay homes in England, Scotland and Wales towards the cost of home renewable heating.

Bare feet walking on a wooden floor with underfloor heating

Air-to-air heat pumps

Air-to-air heat pumps take heat from the outside air and feed it into your home through fans. You need a warm air circulation system to move the heat around your home.

These systems cannot produce hot water and are not eligible for the government's Renewable Heat Incentive payments.

In the summer, an air-to-air heat pump can operate in reverse. In other words, you can use it like an air-conditioning unit to provide cool air for your home.

If you're looking for an air conditioner, check our air conditioner reviews.

Big house next to little house

How much does an air source heat pump cost?

An air-to-water heat pump typically costs between £9,000 and £11,000, according to the Energy Saving Trust. The costs vary depending on the size of the heat pump, the complexity of the system and whether you choose simple or advanced controls (for example a weather-compensated thermostat).

You'll also need to allow for the cost of upgrading your radiators or installing underfloor heating. This can cost several thousand pounds – see underfloor heating costs. You might also need extra insulation.

 Find out how much cavity wall insulation costs.

The main cost of a heat pump is the upfront cost for buying and installing it. The pump will use a small amount of electricity, but the running costs are minimal. Exactly how much your heat pump costs to run depends on:

  • the temperature you want your home to be 
  • the size of your home
  • how well-insulated your home is.

The payback time (how long it takes to recoup the cost of the system in energy savings) depends on:

  • how efficiently your system works (including how well the heat is dispersed and your home retains it)
  • the type of heating system you're replacing
  • whether you get payments from the Renewable Heat Incentive
  • the price you pay for electricity
  • how you use the heat generated by the pump.

The Renewable Heat Incentive (RHI) gives payments to homes which install certain types of renewable heating to help offset the costs. Payments are made over seven years. It will close to new applications at the end of March 2022. Find out more about the Renewable Heat Incentive and how much you could earn.

You could save up to £1,300 a year by replacing an old inefficient (G-rated) LPG boiler with an efficient air source heat pump. 

Old (G-rated) gas boilerOld (G-rated) oil boiler
New electric storage heaters
Old electric storage heatersOld (G-rated) LPG boiler
Figures above show potential annual savings of installing a standard air source heat pump in an average sized, four-bedroom detached home compared with the current heating systems stated. Figures courtesy of Energy Saving Trust website.

But if you’re replacing a newer heating system, an air source heat pump could actually be a little more expensive.

  • Replacing a new (A-rated) gas boiler – £95 - £100 bill increase 
  • Replacing a new (A-rated) oil boiler – £80 bill increase

If you already have an efficient heating system, see more ways to save money on energy bills.

Air source heat pump installation

Air source heat pumps are usually positioned outdoors at the side or back of a property. They need plenty of space around them for air to circulate.

Inside, you'll usually have a unit containing pumps and hot water. It's usually smaller than a standard boiler.

They are less disruptive to install than ground source heat pumps, as they do not require any digging in your garden.

Check first whether you will need planning permission for an air source heat pump. If you live in a listed building, then you'll usually need the consent of your local authority. Also check that your installation will meet the building regulations in your area.

Speak to your home insurance provider too to check if your policy will cover the changes to your heating system.

If you're getting an air source heat pump it's important to make sure that your home is well-insulated so that is can retain the heat. Underfloor heating or larger radiators are often installed alongside heat pumps to disperse the heat better.

Your installer should tell you how to use the controls for your heat pump to help you use it most effectively. You will probably need to heat your home for more hours but at a lower temperature. 

When your system is completed, you should get a Commissioning Certificate from the installer. You should also get an MCS installation certificate once the system has been registered (the installer must do this within 10 days). You'll need this to qualify for most funding schemes.

If you're considering an air source heat pump, use Which? Trusted Traders to find a reliable heat pump installer.

Mother and children sitting beside large radiators

Air source heat pump advantages and disadvantages

Air source heat pumps require little maintenance and can provide heating and hot water, but they aren't flawless systems. Here are some of the key advantages and disadvantages:


  • Energy efficient - air source heat pumps generate less CO2 than many conventional heating systems
  • Less disruptive than installing a ground source heat pump, especially if you're retrofitting
  • Air-to-water heat pumps qualify for Renewable Heat Incentive payments
  • You could save money on heating compared with some older systems.


  • You'll need enough space in your garden for the external condenser unit 
  • Condenser units can be noisy and blow colder air into the area immediately around them
  • Electricity is needed to drive the pump so they're not zero-carbon (unless the electricity comes from a renewable source such as solar panels or a wind turbine).

Are air source heat pumps efficient?

An air source heat pump system can help to lower your carbon footprint as it uses a renewable, natural source of heat – air. How much CO2 you'll save depends on the fuel you are replacing. For example, the figure will be higher if you are replacing coal or an oil boiler rather than natural gas.

A heat pump needs a power source, usually electricity, to power the heat pump, so there will still be some resulting CO2 emissions.

To get the best from your heat pump, you'll need to know how to use it most effectively. Often you'll need to set your heating to come on for longer than with a traditional system. Your installer should show you how to control your heat pump system.

You should also have your heat pump serviced every two to three years. Check that any grills are free of leaves and debris on a regular basis and follow any other maintenance checks advised by your installer.

Heat pump energy labels

Heat pumps must have an energy label on them. It states how energy efficient the pump is on a scale from dark green (most efficient) to red (least efficient).

Since 26 September 2015, all new heat pumps must be sold with an EU product label. The installer should also produce a package label that displays the efficiency based on several different components in the heating system.

All heat pumps certified by the Microgeneration Certification Scheme must be sold with a product label, and the installer must produce a package label. If your heat pump is not sold with a product label, it may not be eligible for the Renewable Heat Incentive.

Read more: tips on saving electricity and money