Enhancing energy efficiency of the heating systems in buildings is one of the major tasks for researchers and professionals in the sector of building comfort systems, because buildings use about 40% of the world's energy. Therein, the use of heat pumps, as the renewable energy source, has a large potential, but it also has some disadvantages that often limit the possibility for the more frequent application. In this paper, the overview of available models for sizing and operation of various types of heat pumps was given. Then, the energy analysis for two single-family house models, each equipped with three different types of the heat pump systems (air-water, ground-water, water-water) was performed. Each energy analysis was carried out for the heating mode using model with hourly method in two typical Croatian climatic conditions – moderate continental (Zagreb) and Mediterranean (Split), supplied in the format of test reference year. The annual heating energy use of the heat pump system was compared to the heating system with condensing boiler. The results were presented in the proper charts. The analysis of investment and operating costs for all system types was performed to show the cost-effectiveness in different climatic and operating conditions. The results showed that the heat pumps present energy efficient but still quite expensive system solution with the shortest calculated payback of 19 years (larger house model in Zagreb, system type water-water, current electricity and natural gas prices). The results indicate that the cost-effectiveness would increase with the capacity. Therefore, if the use of renewable energy sources is in the best interest of the society, small heat pump systems have to be subsidized to stimulate wider utilization. In further research the system utilization in the non-residential large buildings will be analyzed.