Air Source Heat Pump

10 July 2019

An Air Source Heat Pump (ASHP) is a system which absorbs heat from the outside air. This heat can then be used to heat radiators, underfloor heating systems, or warm air convectors and provide domestic hot water in your home.

ASHPs can get heat from the air even when the temperature is as low as -25°C.

In the outdoor unit there is an evaporator (grill with fins), a fan draws air across it, latent heat in the air crossing the evaporator is used to increase the temperature of the refrigerant within the evaporator, the refrigerant is now a gas. Once it has absorbed the latent heat this gas is then passed through a compressor which in turn compresses (squeezes) the gas, this compression cycle of the refrigerant increases the temperature to between 25°C – 75°C. Now the higher temperature gas is passed through a plate heat exchanger this is where the high temperature from the gas is absorbed by the primary water within the heat pump system, this primary water, just like your boiler, is used to heat the house or produce domestic hot water.

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.

An ASHP is installed outside your home, the 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.

The benefits of installing an Air Source Heat Pump:

  • Reduce your heating bills, although as an Air Source Heat Pump uses electricity, you will stay pay for electricity
  • Cut your carbon footprint.
  • Can heat your home as well as your water.

Maintaining an Air Source Heat Pump

An ASHP requires regularly scheduled maintenance but you can expect them to operate for 20 years. You are likely to be advised to carry out a yearly check that the air inlet grill and evaporator are free of leaves or other debris.

Any plants that have started to grow near the ASHP will also need to be removed.

To prevent freezing in a power cut Monobloc heat pumps require anti-freeze to be used.

I’m interested in installing an Air Source Heat Pump, what should I do next?

Search for an MCS certified Installer using our directory of approved installers.

MCS is a mark of quality. Using an MCS certified installer ensures that equipment meets good standards of performance and that installers are technically safe and competent.

Make a decision based on three quotes. Trust your instincts and go with a good value quote with an installer you feel you can trust.

Make sure you receive a design for your new system including the location of your new Air Source Heat Pump. You’ll need enough space in your garden for the external condenser unit (comparable in size to an air-conditioning unit). When considering the location of your new Air Source Heat Pump note that the condenser units will generate noise and also blow out colder air to the immediate environment.