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What fails on a house, why it fails, and what it should cost

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Windows · Fog between the panes

Window seal failure

Fog between the panes means the insulating seal has failed. The window still works. The loss is cosmetic plus a modest efficiency drop, and replacing just the glass is often an option.

Quick answerFog, haze or water droplets trapped between the two panes mean the edge seal of the insulating glass unit has failed. The window still opens, closes and keeps the weather out. What you lose is a clear view and a modest amount of insulating value. Glass-only replacement is sometimes possible and much cheaper than replacing the whole window, and many units carry long glass warranties that survive a change of ownership.

Before you price anything, make sure the moisture is really between the panes. Condensation on the inside surface in winter is indoor humidity, not seal failure, and no new glass will fix it.

1Why insulating seals fail

A double-pane window is two sheets of glass held apart by a spacer around the edge and sealed so the space between them stays dry. Over the years that seal is worked by sun, heat and cold. Once it lets air in, moisture follows, and you see it as fog on the inner faces of the glass.

  • Age and sun. Seals break down gradually, and the sunniest elevations usually go first.
  • Temperature swings. The air between the panes expands and contracts with the weather, which flexes the seal every day.
  • Water sitting at the bottom edge. A frame that holds water against the glass edge wears the seal faster.
  • Impact or stress. A hit, a racked frame or rough handling can break the seal on a newer window.

2How to check what you’re dealing with

  1. Wipe both sidesIf the fog wipes off from the room side or the outside, it’s surface condensation, not a failed seal.
  2. Watch it over a few daysFailed seals show fog or haze that comes and goes with sun and temperature, and often leave a white film or streaks that won’t clean off.
  3. Find the spacer stampLook at the metal or composite strip between the panes for a date or manufacturer stamp. That’s what a warranty claim usually starts from.
  4. Check the frame and sillSoft wood, peeling paint or water marks under the window point to a frame problem that glass alone won’t fix.
Check the warranty before you pay

Many insulating units carry long glass warranties that survive a change of ownership. Look for the spacer stamp between the panes and contact the manufacturer before paying for replacement glass. See broken thermal seal still under warranty.

3Your options

Live with it or DIY

  • It’s one or two windows and the view isn’t critical
  • The frame is sound and the sash works
  • Keep the sill clear of standing water
  • Plan to swap the glass when you do other window work

Call a pro

  • Several windows are fogging at once
  • The glass may still be under warranty and needs measuring
  • The frame or sill is soft or rotted
  • The windows are older and replacement may make more sense than new glass

Replacing the sealed glass unit means removing the glazing stops, setting a new unit made to the exact size and re-sealing it. It’s a measured, made-to-order part, which is why most homeowners leave it to a glass or window shop. If the frames themselves are failing, look at full replacement instead. See single vs double pane if you’re weighing older windows.

4What drives the cost

Glass-only replacement is usually much cheaper than a full new window. The price moves with the size of the glass, any special coatings or tempered glass, whether a warranty covers the unit, how many windows are done in one visit, and access for upper floors. Ask each quote to price glass-only and full-unit replacement side by side so you can compare.

Windows costAll window problems

Several windows fogging?

Talk to a local window pro who will check the warranty stamp and price glass-only replacement before quoting new windows.

877-360-4657

5Questions

Is a fogged window an emergency?

No. The window still works and keeps the weather out. The loss is cosmetic plus a modest efficiency drop, so you can plan the repair.

Can the fog be cleaned out?

Not from the inside of a sealed unit. Once the seal has failed, the fix is a new sealed glass unit or a new window.

Why is my window wet on the inside in winter?

That’s indoor humidity condensing on cold glass, not seal failure. See condensation on the inside in winter.

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.

877-360-4657