The paper assessed the topicality and returns of solar system utilization to heating of water. Practical measurements were conducted after reconstruction of the family house. (in Nesvady, Slovak republic), on which the solar system were assembled. The system consists of the gas heater, solar panels, distributions and circulation pump. The solar system was assembled due to decreasing of operation costs and connected with conventional already used gas heating system by boiler Quantum (V = 115 L). The conventional system was used for 21 days to gather basic values for evaluation. At this point it was observed that 11.93 m3 of gas is needed to heat up 1 m3 of water. Used water in this case was heated from initial 16.14 °C to 52.04 °C of output temperature. Stand by regime of boiler was characterized by 0.012 m3.h-1 consumption of gas. The rest of the measurements represent the annual (from 03/2013 to 02/2014) operation process of boiler Tatramat VTS 200L (trivalent) with 200 litres of volume (as a part of Thermosolar solar system). The solar collectors TS 300 are also part of the solar system. An input and output temperatures of heating water we observed along with water and gas consumption, intensity of solar radiation and actual weather conditions. The amount of heat produced by solar system was then calculated. Total investment on solar system were 2,187.7 € (1,475.7 € with subsidy). Therefore, return on investment for the construction of the solar system was set at 23 years even with subsidy.