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Foggy window between the panes — what it means

Fog or moisture between the two panes means the insulated glass unit's seal has failed and the gas fill is gone — it won't clear on its own. You usually don't need a whole new window: the sealed glass unit (IGU) alone can be replaced in the existing frame, which is cheaper. If the frame is also old or damaged, weigh a full replacement instead.

Why it fogs — and why it won't clear

A double-pane window is sealed with an insulating gas between the panes. When the seal fails, humid air gets in and condenses between the panes where you can't wipe it. Defogging gadgets and drilled vents are stopgaps that don't restore the insulation — the real fix is a new sealed glass unit.

Glass unit vs. whole window

If the frame and sash are sound, replacing just the IGU restores clarity and insulation for much less than a new window. If the window is also old, drafty, or rotting, put the money toward a full replacement instead — see the repair-or-replace page.

When to call a professional

  • • Get a glass shop to measure and quote an insulated glass unit replacement.
  • • If the frame is rotting or the window is near end-of-life, price a full replacement too.

Common questions

Can I fix a foggy window myself?
Replacing an IGU is a job for a glass shop in most cases; DIY defog kits don't restore the seal or insulation. Measure and get a glass-unit quote.
Is a foggy window an emergency?
No — it's a comfort/efficiency issue, not a safety one. Fix it on your own timeline.

Sources

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