Persistent fog between window panes is a sign of failure — here is how to confirm it and what your options are.
Three Signs Your Seal Has Failed
- Permanent fog or haze between the panes that doesn’t clear
- White or chalky residue on the inside surface of the glass
- A noticeable temperature difference between this window and neighbors
What Actually Failed
The spacer at the edge of the glass holds the panes apart and seals an inert gas (argon or krypton) inside. When the seal breaks, the gas escapes and humid air enters. Once it enters, it condenses on cold days and cannot escape.
Your Three Options
- IGU (Insulated Glass Unit) replacement — replace just the glass, keep the frame. Cost: $300–$700 per window in 2026
- Full window replacement — if frame is also aging or rotten
- Live with it — not recommended; efficiency drops 30–50%
Is It Covered Under Warranty?
Most quality vinyl windows from reputable manufacturers cover the IGU for 20 years. Check your paperwork — see our guide on what to look for in a window warranty.
Frequently Asked Questions
Can I clean fog from inside a sealed window?
No — the fog is between sealed panes you cannot access.
How long does IGU replacement take?
Less than 1 hour per window once the glass arrives.
Does foggy glass affect home value?
Yes — home inspectors flag failed IGUs as deficiencies.