Air Source Heat Pumps (ASHP) absorb heat from the outside air for use in radiators, underfloor or warm air heating systems and hot water in your home.
When correctly installed in a suitable property and used correctly, an ASHP can use around a third less electricity for heating than other forms of electrical heating, delivering heat at lower temperatures over much longer hours than a conventional boiler.
How the technology works
A heat pump extracts heat from the outside air in the same way that a fridge extracts heat from its interior. 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 system.
Most ASHPs are sited just outside the property. An electricallydriven fan draws air across an evaporator, cooling the air stream and supplying heat to the heat pump The two main types of ASHP are ‘Air to Air’ and ‘Air to Water’: as the names suggest, one supplies heat to a hot air system that can supply one or more rooms, and the other supplies heat to a more traditional 'wet' distribution
system, either through radiators or an underfloor heating system.
ASHPs can also be used for cooling, removing the heat from the area to be cooled and converting it into useful heat in the form of hot water.
It's possible to take heat from the air when temperatures as low as -15°C, so these systems can work all year round, although in cold weather they will have to work harder to move the same amount of heat indoors, than on a mild day.
There is the possibility of corrosion to an ASHP when sited close to the sea; a corrosiveresistant covering can be applied to the working parts of a heat pump to help prevent corrosion if your property is located in a coastal setting.
You may be able access a grant to support the installation of an ASHP. The eligibility requirements and products supported under government-backed initiatives regularly change. Please get in touch for the latest advice on this.
Choosing your system
The heating requirement for most UK homes is around 6 to 8kW. A normal-sized home (100 sq.m. floor area), built within the last decade, should only require around a 4-5kW heat pump. When correctly installed, for every 3kW of heat provided, an ASHP will consume around 1kW of electricity – this is known as the technology’s Coefficient of Performance (COP).
An ASHP operates at a lower temperature (sometimes as low as 35-40°C) compared to traditional gas or oil fired boilers and therefore usually requires larger radiators than a traditional boiler; underfloor heating is also a popular option to use with an ASHP.
TOP TIP
Heat pumps are always more effective when used in a well-insulated house. If you are considering an ASHP, start with improving the insulation of walls and loft spaces as much as possible. (See our other fact sheets on how to insulate your home.)
Existing radiators can be used with a heat pump system but it's not ideal. The maximum flow temperature that most pumps provide is generally 50°C. If you are planning to use radiators then you will need to select a pump with a higher output than that recommended for underfloor heating.
Planning permission
Domestic Hot Water
It is possible to supply domestic hot water with an ASHP; this assumes a hot water tank is used to store water. The heat pump can be used to preheat water for an immersion heater to boost the temperature.
ASHP installations in England may be considered Permitted Development, so planning permission may not be necessary. Restrictions may apply to listed buildings and conservation areas. Contact Cornwall Council’s Planning department for advice relating to your individual circumstances
