Thermal insulation of standard combined windows with two single panes, which dominate in old buildings, we can increase them by installing a single-chamber double glazing in the inner sash. However, it is heavier than the usual one. The sash and thus the hinges will be heavily loaded. The hinges can be replaced with stronger ones, but it is simply enough not to open the sash so modified or to open it sporadically, only then, when it is really necessary.