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Community and Q&A

Condensation on Insulated Glass windows

user-1067956 | Posted in General Questions on

Is there any correlation between condensation developing on the inside or insulated glass windows that are energy star rated and the low-e film placement? I was discussing the problem that an architect friend is having with two houses recently constructed using a glass with a low-e coating on the interior face of the windows. I told him that the moisture condensation has to do with ventilation not where the low-e film might be in an insulated glass system. Am I off base?

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  1. GBA Editor
    Martin Holladay | | #1

    This issue is referred to as the "Surface 4 low-e coating condensation" issue. The bottom line is that new glazing with a hard-coat low-e coating on surface #4 (the innermost surface of double glazing) is more susceptible to condensation because the surface is colder than it would be if the low-e coating weren't there. Even though the surface is colder, the window performs better than it would without the coating.

    Read all about the phenomenon in this thread: Surface 4 low-e... condensation issues?

  2. user-1067956 | | #2

    Martin: So from what I just read, there is a direct causal effect from the glass coatings, Surface 4 low-e to the condensation. While the window manufacturers are looking into the issue, the customers are complaining. These houses are in zone 5a and the only thing that I can think of to do is to try and get them to increase the ventilation and stop covering the windows.

  3. GBA Editor
    Martin Holladay | | #3

    Yes. If the homeowners increase their home's ventilation rate during the winter, they will lower the indoor relative humidity. And they shouldn't pull their curtains closed if they want to avoid condensation.

    For more information, see Rating Windows for Condensation Resistance.

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