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Foggy Windows? Condensation or A Broken Window Seal.

As soon as fall breaks toward winter and outside temperatures drop, some windows in your home may appear a bit cloudy. Depending on where the fog is occurring, the problem may be as simple as excess moisture developing due to the difference in indoor and outdoor temperature or it might be more serious because the window seal is failing.

WindowCondensation 1


Condensation on the Glass Surface

Condensation on glass surfaces happens, for example, on a hot humid day when moisture may accumulate on the exterior side of your windows. Likewise, on a very cold day, moisture can build up on the interior side of your windows. Condensation on your windows can be worse when the outside temperature is below the dew point of the indoor air. Water or frost appears when warm moist air comes in contact with colder dry air.

Single pane windows or early double-pane wood windows with aluminum spacers can experience condensation. A single pane of glass provides no insulation and the old double-pane design and materials is prone to actually act conduct heat from the inside pane to the outside pane. Today’s windows are engineered much differently and actually reduce any transfer of heat or cold between the two glass panes.

Condensation Between the Glass

Condensation between the glass is a different story altogether. If the foggy surface is between the glass, you likely have a broken seal. The fog may come and go, but eventually the window will be permanently fogged.

Insulating glass seals are designed to withstand the weather – heat, cold, wind, rain and forcible impact. The seal failure rate is very low, but remember, if you have 20, 30, 40 or more windows in your home, chances are high that one or more glass units may fail.Double glazed unit

How Insulating Glass Works

How does insulating glass work? Double-pane glass, known as insulating glass (IG) creates a more energy efficient window. Key to the insulating value is the application of gases (like argon and krypton) and films, extra panes of glass and coatings like Low-E. In fact, these warm to the touch windows actually minimize the potential of condensation on the inside pane, as well as lowering your heating and cooling bills.

IG is created by bonding two panes of glass together, while maintaining a ½ to ¾-inch space between them. Today, most high quality double pane windows have two perimeter seals, an inner seal and an outer seal. Materials designed to keep the panes rigidly spaced and absorb moisture will eventually deteriorate if the seal is leaking moist air between the glass panes. Over time you’ll be left with a foggy window.

Repairing Failed Seals

To repair windows with failed seals you’ll have to either replace the glass units or replace the sash, depending on both the extent of the damage and whether the windows are still in warranty or not. Most high quality windows, like Marvin, Andersen and Pella come with a 20-year warranty for glass seal failure. Some warranties are 10 years. Most manufacturers include their name or ID, as well as a manufacturing date or date code, near the spacer (the material between the glass) or on the bottom of the glass to help you determine whether the window is still under warranty.

Other Suggestions

Fogged windows between the glass can worry any homeowner. As this brief post suggests, the cause can be a broken window seal, but if the fog isn't between the glass it can be related to other factors. To learn more about the causes of moisture build-up on windows read other blog entries such "Condensation and ice-buildup" or "Ask about condensation resistance when replacing windows".

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