There are 2 common types of heat pump available:
Geothermal Heat Pump and Air to Water Heat Pump
This is done by extracting the heat from the air/earth. This heat is then upgraded to a higher temperature, before being delivered to the central heating system and hot water cylinder. Heat pumps also have the ability to do the reverse and provide a cooling system at warmer times of the year.
They are most efficient when linked to a low temperature heat distribution system such as underfloor heating, providing a constant steady temperature. Heat pumps are very economical, capable of cutting your heating bill by up to 70%. For every unit of electricity used to drive a heat pump, you can expect to produce 3-5 units of heat energy.