Paper presents one of the most efficient ways of producing hot water and heating of buildings is the present one, which is the use of an air heat pump. They are often chosen to improve energy efficiency in a building. The principle of operation and main parameters influencing their effectiveness were presented. In addition, the use of heat pumps has been discussed in terms of their choice as a variant in energetic audit. The problems related to the correct device selection at the stage of the audit calculations were discussed. In the final part of the paper, the authors presented a computational example of the air-to-water heat pump selection in the energy audit. Moreover the ecological analysis related to different source of energy in building was presented.