The earth’s surface acts as a huge solar collector, absorbing radiation from the sun. In the U.K, several metres below the surface, the ground maintains a constant temperature of 11 to 13OC. In the winter this temperature is warmer than the air above it. GSHPs are used to extract this heat and transfer it to a building, where heat is required. In the summer months the ground temperature is cooler than the air on the surface. The function of a GSHP can be reversed and used as a cooling mechanism, drawing heat out of a building. For every unit of electricity used to pump the heat, 3-4 units of heat are produced.