Fresh air enters at the bottom of the window. Ambient heat and, on a warm day, sun rays heat the fresh air as it rises up to the valve at the top.

At the bottom of the ventilation window, there is a valve that is permanently open to allow fresh air to enter the cavity between the double glazing and the inner pane. Also at the bottom, there is a storm vent that prevents excessive flow of air when the building façade is exposed to high winds.

On a warm day, the air passing up through the window is so hot that it is not wanted in the building. The valve turns automatically and directs the hot air outside. At the same time, a second valve opens to allow for direct inflow of fresh air.