Symptoms
- Fog, streaks, or droplets visible between the two glass layers
- Cannot be cleaned from either side
- Often worse after temperature swings
- May include white mineral haze over time
Likely causes
- CommonFailed edge seal on the insulated glass unitAge, UV exposure, and temperature cycling break down the seal that keeps the airspace sealed.
- CommonSaturated desiccant in the spacerOnce the drying agent inside the spacer bar is used up, any moisture that enters stays as fog.
- PossibleImpact or stress damage to the sealA hard bump to the frame can crack the edge seal even if the glass itself looks fine.
- PossibleOlder or lower-quality manufacturingSome units are more prone to early seal failure than others.
What to do
- Verify the moisture is between the panes and not on either surface by trying to wipe it away.
- Check the window brand and age; many manufacturers offer a warranty on the sealed glass unit for a decade or more.
- Contact the manufacturer or original installer to see if a warranty replacement applies.
- If no warranty applies, get quotes for glass-only replacement, which keeps the existing frame and sash.
- Compare glass-only replacement cost against full window replacement, especially if the frame or hardware also needs attention.
- Schedule replacement with a glazier or window company, since resealing the failed unit isn't a lasting fix.
- Expect several weeks of lead time if the glass needs to be custom-made to size.
Tools and parts
Replacement insulated glass unitSearch: “double pane glass unit replacement”
When to call a pro
This requires a glass company or window installer; there's no reliable DIY way to reseal a failed insulated glass unit.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.