Air Source Heat Pump

An introduction to air source heat pumps

Air Source Heat Pumps (ASHPs) are becoming commonplace in new build housing and as we transition away from fossil fuels, they will also start to replace traditional boilers in existing homes.


Most heat pumps run at lower flow temperatures than boilers and therefore are ideally suited to underfloor heating systems or larger radiators to ensure the required outputs can still be achieved. This short video gives a brief overview of how they can replace traditional heating systems.


How they work

ASHPs are powered by electricity and require a dedicated connection within the property.


The unit draws in air that is then passed over a refrigerant, which boils at around 40 degrees. The refrigerant gas is then compressed and passed over an evaporator which distributes the heat into a heat exchanger. This is known as the 'refrigeration cycle' and is exactly the same process that happens in domestic fridges.


Buffer tanks or volumisers are common with heat pump systems as heat pumps require a 'minimum system volume' to operate effectively and ensure that they can perform a defrost cycle to melt any ice build up. The defrost effectively reverses the operation and uses the hot water in the pipework to melt the ice.


Different types of air source heat pumps

Monobloc Air Source Heat Pumps


Flow and return pipes are run into the house and connected to the space heating and DHW circuits, often via a buffer tank or volumiser. The pipework must be properly insulated and filled with glycol to prevent freezing in the event of a power failure or breakdown. Monobloc systems are perfect for heating engineers moving into heat pumps.


Split Air Source Heat Pumps


Split pumps have both an indoor and outdoor unit that are connected by refrigeration pipework. Outdoor units are generally a little smaller than other heat pumps, as they do not have any hydraulic components. The indoor unit contains the heat exchanger and pump and looks very similar to a gas boiler. With split systems, the outdoor unit can be installed up to 25m away from the property. Installers must be FGAS registered.



Hybrid Heat Pumps


Hybrid systems utilise a heat pump alongside a traditional boiler. These can work as true hybrids, whereby both systems work at the same time to maximise efficiency, or as a bivalent set up, in which the system switches from the heat pump to the boiler at a pre-set temperature. One key advantage of this setup is that a combi boiler can be used to provide the hot water, removing the need for a heat pump cylinder to be installed.


Adey Pro 3 Filter

How City Plumbing can help you

Through our dedicated, in-house Energy Efficiency team, we can support you with:


  • Full product solutions, from air source heat pumps to ventilation systems and accessories
  • Impartial product advice
  • Fully indemnified design & estimation service
  • One point of contact for all your needs

Browse the range

Browse the range