Ground Source Heat Pumps (GSHP), also known as geothermal heatpumps, provide heating at very high efficiency. The GSHP usually draws heat from a fluid circulating underneath the ground, either in horizontal slinkies at depths of up to 2m, or in vertical loops of pipe (boreholes). The GSHP works like a refrigerator - but backwards - it draws heat out of the ground loop and using a refrigeration cycle compressor, it pumps the heat into the building's heating system. This process is very efficient - typically, a GSHP has a Coefficient of Performance (CoP) of in excess of 4 - ie for every unit of electricity consumed, it produces 4 units of heat. In fact, by optimising the heating system, it is possible to achieve CoPs as high as 6. GSHPs can extract heat from burried loops of pipe, but alternatively, can extract heat from wells, lakes, streams or rivers.