As leaders in the window and door industry, we encourage the public to ask us any questions they might have regarding replacement windows or anything pertaining to our industry. Questions which we feel has helpful information are answered in our “Ask the Expert” section. Here's a question from one of our visitors.

Question from John

My home has pre-painted wood windows that are over 25 years old and still in good shape with no mold or rot. However, condensation exists in the winter even if the inside humidity level is only 40%. Could it be they are not sealing properly or will replacing them solve this?

Response from Our Expert

John, thanks for your question - we get this one a lot when the weather turns cold. Condensation on your window is not a problem unless the condensation is inside the thermal - between the two windows panes. If there is moisture in your thermal then you need to get it replaced.

A close up view of condensation forming on a replacement window.
Pro tip: Condensation on your window is not a problem unless the condensation is inside the thermal (between the two panes). If there is condensation in your thermal, it's time to get your window replaced.

If the condensation is on the glass inside your home that just means the relative humidity in your home is high enough to cause some of the moist air to condense - the same way warm air condenses on a cold soft drink can on a hot day.

Condensation on windows inside your home occurs when when the indoor glass temperature is below the dew point of the room side air.

Certain areas of the home where there is excess moisture, i.e. kitchens and bathrooms, and even bedrooms - where your breathing will make the air more moist, are the most common places to experience condensation. Condensation occurs at the bottom of windows and in the corners because the air flow is weakest in the corners and because when water condenses it is heavy and gravity takes it to the lowest point.

If you see condensation in the middle of the window in a round or elliptical pattern then you should have your windows checked. In this case the two window panels may be too close together.

To answer your original question: condensation on the room side of your window isn't a problem. Condensation between your two window panes is a problem and should be checked.

One other comment regarding wood versus PVC windows - wooden windows will rot if they are not properly maintained over time as moisture build up from condensation might get into the natural fibers of the window if they are not properly painted and sealed. This is one of the advantages of PVC windows - you don't have to worry about the window rotting or molding.

Hope this helps.

Alec Bigras, Verdun Service Manager

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