Air Source Heat Pump – How It Works

An air source heat pump is fitted outside your home, usually near an external wall and can be floor or wall mounted. The external fan extracts heat from the air, even in minus degree temperatures, and converts it into heat for your home. This heat can then be used to heat radiators, underfloor heating systems, or warm air convectors and hot water in your home, it’s up to your decide what you want.

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.


So how does an air source heat pumps function?

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 systems.

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. This makes them 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.


Get more out than you put in

Air source heat pumps are measured by the Coefficient of Performance (CoP), which is the ratio between the amount of heat delivered and the electrical power consumed by the compressor.

With conventional boilers, 1 unit of input energy provides less than 1 unit of output heat. But with a air source heat pump, the conversion of renewable heat into useable energy means that for every unit of electrical input energy, 3 – 4 units of heat output are produced by the heat pump.

The amount of heat output produced for every unit of input energy varies constantly dependent on a number of factors. A well-designed system should achieve an average CoP over the year of more than 3 when used to produce heating and hot water. Meaning you are getting far more energy out than you are putting in.


For a more in-depth understanding of how air source heat pumps work, take a look at our heat source pages on our website.

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