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What is an Air Source Heat Pump System?

Air source heat pumps are a renewable heating system that extract heat from the air outside to provide heating and hot water around the home. They can operate in temperatures as low as -15°C to deliver a highly efficient way of heating the home while helping to reduce energy bills.

With this guide you'll find out exactly how air source heat pumps work and see if one could benefit your home before getting installation quotes.

How air source heat pumps work

The appliance itself is installed outside and a fan within the pump rotates to bring air inside then:

  • The air passes over an exchanger coil which contains a refrigerant fluid
  • The fluid boils and evaporates which transforms into vapour
  • Vapour is compressed at a high temperature to produce heat

Once the heat has been produced, it can then be used for your home's central heating and hot water.

Essentially, they work in the same way as fridges or air conditioning but generate warmth from cold air rather than the other way around.

Types of air source heat pump

Air-to-air heat pumps

Air-to-air heat pumps heat your home by extracting heat from the air outside which is then circulated around the home using fans. In the summer months when the temperature increases, the system can be used to cool the air in the home. This type of heat pump can't be used to produce hot water.

Air-to-water heat pumps

By extracting heat from the air outside, an air-to-water heat pump heat your wet central heating system, underfloor heating and hot water cylinder. They're at their most efficient when operating at lower temperatures for a lengthy period, rather than a higher temperature for a shorter time.

There are many different models for both types of air source heat pump so to find the right one, start comparing ASHPs with our comparison article.

Best heating systems for air source heat pumps

As air source heat pumps are at their most efficient when operating at low temperatures, it's recommended that they're installed with large radiators or underfloor heating systems.

Underfloor heating only requires temperatures of about 30°C to heat a room while a radiator needs to reach temperatures of approximately 70°C. If you'd like to combine an ASHP with radiators then you should consider fitting larger ones as they have more surface area which means they don't need the higher temperatures that standard radiators do.

Can a heat pump keep my home warm?

As mentioned above, ASHPs operate at a lower temperature to increase their efficiency which means that the temperature won't be as high as with a boiler. Help to increase the temperature of the hot water further by adding an immersion heater into the hot water cylinder.

In order to hold onto as much of the heat being generated as possible, it's vital to ensure that your home is well insulated to prevent any heat escaping. This may add to the costs if your home isn't already well insulated but is well worth doing in the long run. You can find more Air Source Heat Pumps: Advantages & Disadvantages.

As well as heating the property, an air source heat pump can also be used for cooling during the warmer summer months. Plus, if you have a swimming pool, they can warm up the water too.

How efficient are air source heat pumps?

Heat pumps are highly efficient heating systems that can produce 4 kWh of heat for every 1 kW of electricity needed to power the heat pump. That’s an efficiency of 400% which is incredibly efficient when you consider that gas and oil boilers can achieve a maximum efficiency of around 94%.

Air source heat pump efficiency is measured in two ways:

  • Coefficiency of Performance (COP): This tells you how much heat the heat pump will produce per unit of electricity used.
  • Seasonal Coeffficient of Performance (SCOP): This is the average COP across all 4 seasons and will let you know how efficient the unit will perform in any given season.

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How a heat pump can earn you money

The Renewable Heat Incentive (RHI) is a government scheme that was set up to encourage homeowners to install renewable technologies. With an eligible renewable heating system installed, you can receive quarterly payments every quarter for 7 years.

You won't be able to benefit from the scheme with an air-to-air heat pump but by having an air-to-water heat pump installed, you can benefit from these quarterly payments.

To help give you an idea of how much money you could earn through the RHI with an ASHP, we did some calculations using the government's BEIS Domestic Calculator*.

Detached Home (3 bedrooms) RHI Payment per Quarter Annual RHI Payment Total RHI Earned Over 7 years
Replacing Gas or Oil System installed pre 2005 £213 £850 £5,950
Replacing Coal Fired System £220 £880 £6,160
Replacing Other Electricity System £183 £730 £3,920

*Tariff of 10.49p / kWh (valid for applications received before 01 October 2018). Based on a home located in England or Wales, built between 1976 - 1982, unknown amount of loft insulation and cavity walls with insulation. The calculations are intended as a representation only.

The government have announced that the RHI is due to come to a close on March 31st 2021 to domestic installations but is due to be replaced by the Clean Heat Grant the following year (2022).

Is an air source heat pump right for your home?

If your home has a highly efficient gas or oil boiler installed then an ASHP won't be of any real benefit in terms of energy savings. The ideal homes for ASHPs are off-grid, well insulated properties or new-builds.

The appliance needs to be installed outside in an area clear of obstructions and if you live in England or Scotland then you won't require planning permission as long as the installation meets certain criteria. Homeowners in Wales and Ireland must seek planning permission.

For homes with large radiators, underfloor heating or other heating systems with a lower operating temperature, then an ASHP is the perfect partner. To ensure that your home is being heated effectively it must be well insulated.

Air Source Heat Pumps: Advantages & Disadvantages

Find out how your home can benefit from the air outside.

Find out more

Best Air Source Heat Pump Manufacturers

Make sure you install the best system for your home.

Find out more

Air Source vs Ground Source Heating Systems

Compare two renewable heating systems to find out which one's right for your home.

Find out more




About the author


Adam is our resident home heating expert. His experience and advice has helped millions of customers improve the efficiency of their homes and save money.

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