A ground source heat pump takes heat from the ground and transfers it to your home in a process similar to that used in a domestic fridge. This is a well proven technology which has been used for many years although has only recently grown in popularity. Modern heat pumps can have efficiencies in excess of 500% which means for every 1kW of electricity they consume, you get 5kW of heat into the house.
In practise the efficiency is highly dependant on the temperature required so it’s important to match the heating system to the heat pump. Generally the lower the flow temperature, the higher the efficiency so underfloor heating and low temperature fan assisted radiators are ideal.