Ground-source heat pumps (GSHPs) draw heat from under the ground using either a borehole or a series of pipes laid a few metres below the surface. This
heat is mainly solar energy that has been absorbed by the ground. The ground below a couple of metres down is protected from extremes of heat or cold and stays at about 10°C all year. This is of course not warm enough in itself - the heat pump ‘boosts’ it to the level needed for heating a home.
Air-source heat pumps (ASHPs) do the opposite of air-conditioning units. Instead of taking heat out of a building, they take heat from the outside air and uses it to heat a house. See our related questions to see which one is right for you.