There are several types of heat pump. All use the same basic principle of extracting heat from a source and concentrating it to obtain a higher temperature, usually then applied to water for domestic heating and hot water.

The device which does this can be thought of as a refrigerator operating in reverse. It is powered by electricity, but the amount of heat energy delivered is several times more than the electrical energy consumed. The ratio of the output to the input energy is called the Coefficient of Performance (COP).

As heat pumps transfer rather than produce heat they are more efficient than traditional heating systems.

Ground source heat pumps

Obtain their heat energy from the ground. The temperature of the soil even just a metre down is very stable throughout the year in the UK.

The ground heat is captured using water passed through pipes buried in the ground. These can be either coils burried in the topsoil, or one or more boreholes sunk deeper into the subsoil.

Air source heat pumps

Obtain their heat from the ambient air, using a fan unit located outside the building. The pump converts heat from the air into more useful energy through a heat exchanger.

Air source heat pumps can save more than 2 tonnes of carbon a year, emitting 50% less than gas boilers and 70% less than electric systems.

As well as being used to heat in winter their cycle can be reversed to cool in the summer, when the unit takes heat out of the indoor air and releases it outside. 

Water source heat pumps

These are rather rarer, using heat from a pond, lake, river stream or other body of water, to provide heating for nearbly homes.

The water is drawn in to the pump's heat exchanger, where the heat is extracted and the water is returned to the source.