A local representative for a national window manufacturer asked if we could investigate several instances where clients with new window installations were experiencing condensation on the interior of the window glass.
Investigation: Each of the several homes with this condition was examined during cold weather when the moisture was actually present on the windows. Relative humidity levels were recorded as well as interior surface temperatures of the windows and exterior walls. In all cases elevated levels of moisture were found to be present in the range of 50% R.H. or higher. At an interior air temperature of 70 degrees and relative humidity of 50%, the dew point is about 52 degrees. Most window surfaces colder than this in the winter, resulting in condensation.
Recommendations: Find sources of excessive moisture in the house that contribute to elevated levels of humidity and remove or remedy them. These sources can be unvented bath fans, dirt crawl spaces, water leaks and others. Fixing these will lower the relative humidity level and stop the condensation on windows.
Results: In all cases, moisture sources were discovered that were the causes for elevated relative humidity readings. In each case, home owners were given specific direction on how to eliminate the problem.