How do drapes and window shades affect window condensation?

Drapes and other window coverings can contribute to a condensation problem by restricting the flow of warm room air over glass surface. Therefore, indoor condensation is more apt to occur when the drapes are closed or the shades are pulled down. Why does a 1"-wide strip of condensation sometimes form all the way around the window? If a strip of condensation forms all the way around the window, chances are good that the unit features metal components that are transmitting cold from the outside to the inner glass, cooling the glass surface where the condensation forms. In effect, the center of the glass stays warmer than the glass close to the edge. This strip of condensation doesn't mean the window is leaking air or not working properly. What causes condensation on the inner surface of storm windows? All operating windows leak some air between the window frame and sash. So when warm household air seeps in around the sash and becomes trapped by the colder storm window, condensation ...  more