Researchers are rather closely involved in Solar Combisystems recently, but there is lack of study that presents the optimum design parameters. Therefore, in this study the influence of the four major variables, namely; outside, inside temperature, solar radiation on horizontal surface and instantaneous efficiency of solar collector on the energetic, exergetic and environmental efficiencies of Solar Combisystems are investigated and system optimization is done by a combination of response surface methodology. Measured parameters and energetic-exergetic and environmental performance curves are found and statistical model is created parallel with the actual data. It is found that statistical model is significant and all "lack-of-fit" values are non-significant. Thus, it is proved that statistical model strongly represents the design model. Outside temperature, solar radiation on horizontal surface and instantaneous efficiency of solar collector are the decisive parameters for all responses but instantaneous efficiency of solar collector is not for environmental efficiency. Maximum exergetic efficiency exceeded 11%, maximum environmental efficiency reached up to 95% at optimized process. The optimum value of the outside temperature and solar radiation are found as 22 degrees C and 773 W/m(2) for all responses, on the other hand optimum collector efficiency is found around 60% for energetic and exergetic efficiency values. Inside temperature is not a decisive parameter for all responses. (C) 2015 Elsevier Ltd. All rights reserved.