The simulation research results of gains, losses and heat balance of two-, three- and four-paned windows positioned at 30, 60 and 90° angles relative to a surface for climatic conditions in Poznań and the Greater Poland region expected in the eco-power industry have been presented. It has been shown that in a summer period the increase in a number of panes and the angle of widows decreases high solar heat gain which determines similar alternations of heat balance at low losses. Particularly high window heat balance occurs from May to August due to high sun exposure at low heat losses. In winter, window heat balance is generally positive, apart from December, when it is minor and negative due to the lowest solar radiation at not the lowest outdoor temperature. Increasing a number of panes and a window angle does not change significantly window heat balance in a winter period.