This study aims to determine how the variable operating parameters affect the efficiency and operating costs of the heat pump. A single-family house with a design heat load of 4,3 kW located in climate zone IV in Bialystok is analysed. The analysis concerns a brine-to-water heat pump and an air-to-water heat pump. Three values of bivalent temperature are assumed for the air source heat pump: – 10, – 9 and – 8°C. Five values of heating water temperature are considered: 35, 40, 45, 50 and 55°C. The basis for calculating the heat output and electricity consumption of the heat pumps is the outside air temperature determined for each hour of the heating season in the statistical year. The SCOP values are calculated. Electricity consumption and its cost are determined according to three tariffs offered by PGE: G11, G12 and G12w. A ground source heat pump ensures the lowest operating costs and highest SCOP values. In an air source heat pump the lower the bivalent temperature, the lower the operating costs. The most favourable electricity tariff is the weekend tariff G12w. The 24-hour tariff G11 with identical charges during the day and night is not recommended to use for heating purposes.