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Why is My Double-Pane Window Fogging?

Why is My Double-Pane Window Fogging?

Maybe this has happened to you. One morning you are cleaning the windows and you come across a smudge that won’t wash away. You try cleaning it from the inside and outside without success. Then you realize, it isn’t a smudge at all. It is fog stuck between the two panes of glass. During the day it disappears, but then it reappears. How did it get there? Is it bad? How do you get rid of it? Here is everything you need to know about condensation between your double-pane windows:

What are Double-Pane Windows?

By nature, glass is not a natural insulator. It allows heat and light to transfer through unimpeded. That is why most windows today have at least two panes of glass. They are separated by spacers and sealed together as a single unit called an insulated glass unit (IGU). They work to slow down thermal transference and improve the efficiency of your windows. But that isn’t normal oxygen sealed between the panes of your windows. It is a special gas fill.

What is a Gas Fill?

It is an odorless, colorless, non-toxic noble gas sealed between the panes of an IGU. The gas has more density and does not transfer heat as readily as oxygen, making modern windows more efficient than ever. Manufacturers typically use one of three noble gasses—argon, krypton, or xenon. Argon makes up approximately 1% of the atmosphere and is one of the most inexpensive and popular gasses used in IGUs. It improves a window’s u-value by 16% or more. Krypton and xenon can improve the u-value by 27% or more, but these gasses are not as readily available and more expensive.

Why is Condensation Forming between the Panes?

Windows deal with an onslaught of cold, heat, wind, rain, and debris. And while the noble gasses are more stable than air, there is still some thermal expansion and contraction. This causes “solar pumping” which puts pressure on the window seals. Usually, it happens to windows on the sunny side of the house first because the heat accelerates seal failure. Given enough time, the seals on IGUs will break down and fail. The noble gas leaks out and normal, water-laden air replaces it. The silica beads installed in the windows can absorb some moisture, but eventually, they will become saturated. There will be enough moisture caught between the panes and fogging will occur.

Is Fog Between the Panes Cause for Concern?

Because it comes and goes, most homeowners don’t worry about fogging between their window panes. But this type of condensation can lead to water damage, mold, and rot. Especially when the moisture starts to freeze and melt in the winter, making the cracks even larger.

What Can I do about Double-Pane Window Fog?

There is not an easy fix and you will need to contact a window professional. One solution might be to drill a hole in the assembly and insert a valve that works to remove the moisture. With this option, you may not have any more problems with fogging, but the window will not work as efficiently. You might get lucky and be able to replace just the glass. This solution depends on the age, type, and manufacture of the original window. But more often than not, your best solution is to replace the entire window. It is the only way to eliminate condensation and restore efficiency.


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