 Air-water heat pumps are otherwise similar to air-air heat pumps, but they transfer the extracted heat into a water heating circuit, floor heating being the most efficient, and they can also transfer heat into a domestic hot water tank for use in showers and hot water taps of the building.However, ground-water heat pumps are more efficient than air-water heat pumps, and therefore they are often the better choice for providing heat for the floor heating and domestic hot water systems.Air source heat pumps are relatively easy and inexpensive to install and have therefore historically been the most widely used heat pump type.