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Windows · You can handle this one

Fog between the panes

A failed insulating seal. The window still works. The failure is cosmetic plus a modest efficiency loss. Glass-only replacement is sometimes possible and much cheaper than the full unit.

Quick answerDouble- and triple-pane windows are sealed units with a spacer around the edge. When that edge seal fails, moist air gets between the panes and condenses, leaving fog or a white film you can’t wipe off. The window still opens, closes and keeps out weather. You lose some insulating value and a clear view. Check for a warranty first, then price replacing only the glass unit. You can handle this one yourself. No call needed.

A fogged window looks like a broken window, and that’s how people end up buying a whole new one. In most cases the frame and sash are fine, and only the sealed glass unit needs replacing.

1Why the seal fails

  • Age. Edge seals weaken over years of heating and cooling cycles.
  • Sun and heat. Units in strong sun work their seals harder.
  • Water at the edge. Glass that sits in water, from a blocked weep or a poorly drained frame, fails sooner.

2How to check

  1. Wipe both sidesIf the fog stays after you wipe the inside and outside, it’s between the panes.
  2. Find the spacer stampLook at the metal or plastic strip between the panes. Many have a manufacturer name or date printed on it.
  3. Look for paperworkCheck your closing documents or the window brand for a glass warranty. Many survive a change of ownership.
  4. Check the frameIf the sash and frame are sound, glass-only replacement is likely an option.

3Fixing it

Do it yourself

  • Check the warranty before paying anything
  • Measure the glass and call a glass shop for a glass-only price
  • Live with it if the view doesn’t bother you; it’s not urgent

Hire a pro

  • Install the replacement glass unit
  • Replace the sash if the frame design won’t allow glass-only
  • Check drainage if the glass was sitting in water

Be wary of fixes that drill and vent the unit to clear the fog. Ask how long the result is guaranteed, in writing.

4What drives the cost

Glass size, glass type (low-e, tempered, laminated), whether the frame allows glass-only replacement, and the height of the window. A warranty can reduce the cost to labor only, or to nothing.

Windows cost

5Questions

Is a fogged window an emergency?

No. It still keeps out weather. It’s a comfort and appearance issue you can plan around.

Do I need a whole new window?

Usually not. The sealed glass unit can often be replaced on its own.

Is it covered under warranty?

Possibly. See broken thermal seal still under warranty.

Written by Jaylan Jones. I Like To Exterior Services earns a referral fee when a call connects to a contractor. See our business-model disclosure.