heat pump

A heat pump works on the same principle as a refrigerator or an air conditioner. A compressor drives a refrigerant around a cycle: one heat exchanger takes heat in from a source, such as the surrounding air, the ground or water, and another releases it into the building, where it is delivered as warm air or through a water based system such as radiators.

Because the machine moves heat rather than generating it, it delivers more heat than the electricity it uses. The International Energy Agency puts the coefficient of performance of a typical household heat pump at around four, meaning about four units of heat for every unit of electricity, which makes current models three to five times more energy efficient than gas boilers.

Many heat pumps can also provide space cooling in summer.