In climate zones of Turkey, it is not sufficient to heat service water, swimming pools and houses by solar energy only, throughout the year. Therefore designing solar systems, which can be operated combined with another heat generator, is much more appropriate. In this study; two different systems have been installed to perform thermal performance analysis of a 198 m² building which is heated by the energy supplied from evacuated tube solar collectors, that are used as solar energy collectors and by an auxiliary heater. In the first system, evacuated tube solar collector was placed inclined with an angle of 40º from the horizontal plane and electrical resistance in the boiler tank was used as auxiliary heater. In the second system, evacuated tube solar collector was placed perpendicular to the horizontal plane and any auxiliary heater was not used. Experiments of heating a space by the installed systems were performed in October 2008, November 2008 and January 2009. In this context, the experiments performed in October 2008 showed that the whole energy demand for space heating could not be met without auxiliary heater. Based on this, auxiliary heater in the inclined collector system was put into operation in November 2008 and January 2009. The experiments were performed, results of the experiments were compared and system performances were determined by comparing the rate of energy supplied from collector systems to the energy demand. Also the evacuated tube solar collector efficiencies were calculated by using the data obtained from the experiments.