An effective way of reducing the transmission flows through windows during the heating season is to use the air extracted from the room to ventilate the air space between the glazings. The heat transmission coefficient of a ventilated window is between two thirds and one third of that of an unventilated window, and the infiltration heat loss is less. Proposes analytical dependencies and graphs for the determination of the heat transfer coefficient and the temperatures of the panes as a function of the window construction and the heat transfer intensity. Derives the minimum air exchange which prevents condensation on the inner panes. Finds the calculation results agree well with experimental results.