Windows & blinds

Fogged double-pane window (foggy inside the glass)

Fog trapped between the two panes means the seal has failed and moisture got in; cleaning won't fix it, and the insulated glass unit typically needs replacing.

Difficulty
Professional only
Time
1–3 hours per window (professional)
DIY cost
$0
Pro cost
$150–$500 per window

Symptoms

  • Cloudy or foggy area between the panes, not the surfaces
  • Fog doesn't wipe away from either side
  • Sometimes visible mineral streaks or condensation droplets inside the glass
  • Usually appears gradually, worse in cold or humid weather

Likely causes

  • CommonFailed insulated glass unit sealThe edge seal that keeps argon gas in and moisture out has broken down with age.
  • CommonDesiccant inside the spacer saturatedThe moisture-absorbing material in the spacer bar has reached capacity and can no longer keep the airspace dry.
  • PossibleManufacturing defect in the sealSome units fail years earlier than expected due to a bad seal from the factory.
  • PossibleTemperature extremes stressing the sealRepeated expansion and contraction can accelerate seal failure.

What to do

  1. Confirm the fog is between the panes by trying to wipe both the inside and outside glass surfaces; if it stays, the seal has failed.
  2. Check whether the window is still under manufacturer warranty; many carry 10–20 year glass warranties.
  3. Get a quote for a glass-only replacement (just the insulated glass unit) rather than a whole new window, which is much cheaper.
  4. If the frame and hardware are in good shape, glass-only replacement is usually the most cost-effective fix.
  5. For a temporary appearance fix, some companies offer defogging services that drill and reseal the unit, though results vary and aren't permanent.
  6. If several windows in the house are the same age and starting to fog, consider budgeting for the rest since they're likely near the same lifespan.
  7. Once replaced, expect the glass to stay clear for many years if the new seal is installed correctly.

Tools and parts

Replacement insulated glass unitSearch: “double pane glass unit replacement”

When to call a pro

This is a job for a glass company or window installer since it requires precise measurements and sealed unit fabrication; DIY glass replacement is not practical for most homeowners.

Safety

Generally low risk

Generally low risk for a careful person. Stop if anything looks different from what this guide describes.

Related guides

Operator provides AI-generated troubleshooting information. It can be wrong. For safety-critical, electrical, gas, structural, medical, automotive safety, or other high-risk problems, consult a qualified professional.