How does an air source heat pump work?

How does an air source heat pump work?

Air source heat pumps, sometimes known as air-to-water heat pumps, work as follows:

A fan blows air across a heat exchanger containing a very cold refrigerant liquid in the external ASHP unit. As the refrigerant is warmed (it will do so even if the air is as cold as -15°C) it turns into a gas, this gas then passes through an electrically driven compressor where the compression of gas generates heat. The low grade heat from the outside air is therefore converted to high grade heat suitable for use in the home. The higher the output temperature that is required (poorly designed radiators for example) the harder the compressor has to work to produce the higher temperatures, demanding more electricity in comparison to the energy brought in from outside.


A well installed air source heat pump should roughly require 1kWh of electricity for every 3kWh of heat it produces. By well installed that means the radiator or UFH circuit requires no more than a 50°C flow temperature at -3°C outside. Spire Renewables offer a service where an existing radiator system can be surveyed to work out if it will run at a 50°C flow temperature. It is by no means a presumption that an existing radiator system is undersized – in fact it is common that radiators are often substantially oversized in order to work with a conventional boiler heating philosophy.

If you live in a property where potentially the existing radiator system is undersized, we offer a pre-plumbed, pre-wired hybrid air source heat pump kit. Here the heat pump runs down to 3°C, and below this the existing fossil fuel boiler kicks in. The fossil fuel boiler also continues to run hot water in the property. This should mean the heat pump will cover at least 95% of the buildings required heating load per year. In comparison to an oil or LPG fired system, your bills will be reduced and the carbon saving will be substantial.

An air source heat pump installation requires no digging or drilling, few plumbing connections are used during installation and operate in temperatures as low as -15°C making them a financially effective option for those sites off mains gas, especially with the BUS grant, where you can receive £7,500 off the cost of your air source heat pump.


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