An air source heat pump is a device that has three primary parts:

There is the evaporator coil which is able to absorb heat from the outside air; the compressor pumps a type of refrigerant through the heat pump, then compresses the gaseous refrigerant to the proper temperature for heat distribution; and, the heat exchanger will then transfer the heat made available through the refrigerant to either air or water. The air-to-water system will then make it possible for the heat to be used to heat water which can preheat water within a storage tank, or it can circulate through the underfloor of a building or can simply be redirected to radiators. Heat pumps will produce very hot water which will actually be at a lower temperature (typically 35-45o C) than what is typical of standard boiler systems, which then will make the underfloor heating very effective. Additionally, the air-to-air system can be used to produce warm air which is circulated by fans that are part of the system that can heat an entire building.