In this study "design parameters" and efficiency effect of basic system components on exergetic efficiency of "Solar Combisystems (SCS)" which can be named as a new generation space heating systems are investigated in order to determine the optimum operating values of system components. The effects of four variables, instantaneous exergetic efficiency of solar collector (eta(Excoll)), heat exchanger-1 (eta(Exhe-1)), heat exchanger-2 (eta(Exhe-2)) and heating system (eta(ExHs)) on the overall exergetic efficiency of SCS are investigated based on central composite design (CCD) and quadratic models are developed to correlate the variables to overall system net and gross exergetic efficiency. From the analysis of variance (ANOVA), the most influential factor on each experimental design response is identified. It is found that, (eta(Excoll)), (eta(Exhe-1)), (eta(Exhe-2)) and (eta(ExHs)) are statistically significant for net and (eta(Excoll)), (eta(Exhe-1)) and (eta(ExHs)) are statistically significant for gross exergetic efficiency of overall system. Binary interaction effect of independent variables are investigated and it is found that (eta(Excoll)) and (eta(Exhe-1)) is the most important couple that effects the net exergetic efficiency of the system. Net and gross exergetic efficiency of overall system reach to 12% and 14.6% individually, within the optimum values of the variables. (C) 2015 Elsevier B.V. All rights reserved.