Operation tests of an air heat pump used for domestic hot water (DHW) heating were performed. The influence of the supply air temperature in the evaporator cycle and the variable heat load of the condenser on the heating power of the heat pump and the coefficient of performance (COP) was evaluated and discussed. In order to ensure conditions for efficient compressor operation, it is advisable to gradate the heat load of the heat pump using a circulating pump with smooth capacity regulation. The economic analysis demonstrates that the usage of air heat pumps for DHW in comparison with installations equipped with solar collectors provides no measurable economic benefits.