An air to water heat pump is usually placed outside at the side or back of a property, and takes heat from the air and boosts it to a higher temperature using a heat pump. A heat pump works a bit like a refrigerator in reverse. The process consists of an evaporator, a compressor and a condenser. It absorbs heat from the outside air and the heat pump compressor then increases the temperature of that heat further to create useful heat. This heat is then used to heat radiators, underfloor heating systems or even warm air convectors and hot water in your home.  The pump needs electricity to run, but the idea is that it uses far less electrical energy than the heat it produces.