An air source heat pump (ASHP) is a type of heat pump that can absorb heat from outside a structure and release it inside using the same vapor-compression refrigeration process and much the same equipment as air conditioners but used in the opposite direction. Unlike an air conditioning unit, most ASHPs are reversible and are able to either warm or cool buildings and in some cases also provide domestic hot water.

In a typical setting, an ASHP can gain 4 kWh thermal energy from 1 kWh electric energy. They are optimized for flow temperatures between 30 and 40°C (86–104°F) suitable for well insulated buildings. With losses in efficiency, an ASHP can even offer a full central heating solution with a flow temperature up to 80 °C (176 °F).

Air-to-water heat pumps use radiators or underfloor heating to heat or cool a whole house and are often also used to provide domestic hot water.

Air-to-air heat pumps are simpler and slightly more efficient devices that provide hot or cold air directly to internal spaces, but do not usually provide hot water.