radiant energy absorbed by films 22 and 24 on surfaces 21 and 23 increases the temperature at such surfaces and the heat is transmitted to the air in chamber 17 by conduction passages 27 are provided in supporting structure c so that unheated air from the outside atmosphere a or the adjacent interior area b may be drawn into chamber 17 and so that the heated air in chamber 17 may be withdrawn and discarded or its increased heat energy content utilized elsewhere withdrawing the heated air from chamber 17 tends to cool the surfaces 21 and 23 and hence decreases the rate at which heat is conducted from film 24 on surface 23 through pane 13 and into the adjacent interior area b hence it further increases the efficiency of the invention by insulating the adjacent interior area b from excess heat build up resulting from the incident solar energy fig2 shows a typical installation of window unit 11 in a building supporting structure c is located in an exterior wall g of the building between a floor d and a floor e of the building as described in connection with fig1 the window unit 11 separates the outside ambient atmosphere.