Published on February 22nd, 2016 | by Henri


Windows sweat in cool weather

Q.   I have had replacement windows (double sash w/insulated glass) installed in my house approximately 1-1/2 yrs. now. In the master bedroom there are two windows, one on each exterior wall. Now that it’s cold out, the windows sweat. In the morning they are both covered with moisture (only the bottom half of the window) and need to be dried off or mold will occur on the bottom plastic rail. Any idea why this is happening? None of my other windows in the house are doing this.

A.    There may be several reasons for the condensation on the lower sashes. You may keep the bedroom temperature lower than in the other rooms. You probably have a master bath next to the bedroom, and showering will add considerable moisture in both rooms. The reason only the lower sash is affected is because warm air rises, stratifies and the air temperature gets cooler closer to the floor. The room air in contact with the upper sash is warm enough to prevent condensation.

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