Causes of Window Condensation, and What to Do About It

Evan GUncategorized0 Comments


wet windows with condensation inside the home

Good news—sweaty windows can actually be a sign your home is well insulated!


But foggy or wet windows can also mean failed seals in your insulated glass. And that means air leaking from your windows, causing uncomfortable drafts and higher energy bills.

How to Tell Failed Windows from Healthy Ones

When your windows are insulating effectively, a quick change in temperature can make them sweat with condensation. Condensation forms when the glass is cooler and drier than the air around it: for instance the warm, humid air inside your home.

If you can wipe your windows and get the water off, it means they’re probably sealed and insulating effectively, meaning you don’t have a problem.

If you can’t wipe the water off your windows, it may be inside the insulated glass unit of the window, indicating a failed seal. Although it’s not an emergency, it should be addressed as soon as practical. Check out our Glass Replacement page for more information!

Milgard Video: How to Check for Window Condensation

Video Transcript

  • Safety glasses
  • Gloves
  • Soft cloth
  • Glass cleaner

Condensation is a normal part of owning high-quality, energy-efficient windows. Condensation is basically when humid air turns to water droplets on a cold surface.

Windows are a natural place for these droplets to form, since they are a barrier between inside and outside temperature differences. There is natural condensation that all windows will get from time to time, and there is condensation that is formed from a faulty glass unit.

To check which condensation you have, use a soft cloth and gently wipe the interior. If water droplets don’t come off, then use a cloth on the exterior and gently wipe. Natural condensation should wipe off from either the interior or exterior.

If the condensation doesn’t wipe off, then condensation is most likely due to a glass unit failure. If this is the case, please contact the Milgard Service Department to discuss the faulty glass unit and for replacing.

What Failed Glass in a Window Looks Like

foggy failed glass in a home window — patches of hazy condensation and mineral deposits indicate insulated glass unit seal failure

Depending on the air around the window, and the size and location of the leak, insulated glass with a failed seal may appear as:

  • Foggy or patchy
  • Wet and streaky
  • Swirly and/or discolored
  • Hazy with mineral deposits

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