The first major temperature shift of the season is finally here. This typically coincides simultaneously with the first chance your home has of drying out for the winter season – and we see it present as condensation on windows. But is condensation always bad? Because we get so many calls about condensation at Wrightway Home Improvements we wanted to take a quick look at what causes window condensation.

Temperature always seems to be the first sign of winter’s impending arrival. We stop hitting 50 degrees, then 40, then…..the dreaded 30 for a high. As the air begins to cool, we often forget that it can’t hold as much moisture. Usually this isn’t noticeable for us as we head outdoors because we grab a jacket and focus on staying warm enough until the car warms up. There’s a major change that’s happening at the same time that has to do with relative humidity.


Relative humidity (RH) is the amount of water in air at a certain temperature compared to the maximum amount of water that same air can hold at a certain temperature. We represent it as a percentage. Complete saturation would be 100%.

The reason this is important to the transition period in the fall/winter and winter/spring periods is that the air on the inside of the house can experience significant humidity gradients between the inside and outside a home. The humidity and temperature swing can cause condensation to occur in many situations with windows and storm doors. Usually we see this on the bottom edge of the glass because cold air falls and creates a moisture trap with the warmer inside air. This is a similar phenomenon to condensation on a glass of ice water in the summer.



The major concern that most homeowners have when calling us about condensation is – Are my windows bad because I condensation? We like to talk through the appearance of condensation with questions like:

  • Is it consistent on all windows in the home?
  • Is there ice on any of the glass or window frames?
  • What is the humidity in the home? In the winter it should be between 30-40%
  • Has the water started to deteriorate the sash frame due to long term exposure?
  • How long have you been seeing condensation present?

Depending on the answers to these questions, we can usually come to a helpful conclusion for most homeowners. Sometimes it is a “wait it out” scenario as the home slowly dries out. Sometimes it is a faulty weatherstripping or window lock. Sometimes it means exploring replacement windows or replacement doors. If there is active rot or mold because of repeated exposure to window sweat, it may be time to get a low maintenance replacement window to remedy the problem.

We hope this post helps explain what causes window condensation in the winter months in the the Fox Valley and Fond du Lac.



Wrightway is the Marvin Infinity Windows dealer in the Oshkosh, Fond du Lac, and Appleton, WI territories. We have an expansive service area and we are experts in replacing siding, windows, and gutters and installing gutter guards. Replace your windows today and free up some of your time for more important things. Find out more at