How to Tell If Your Window Seal Has Failed — And What It Costs to Fix in Toronto (2026)

If you've noticed a cloudy haze, streaks, or condensation trapped between your window panes — condensation you can't wipe away from either side — your window seal has likely failed. It's one of the most common window problems GTA homeowners face, and the good news is: you almost never need to replace the entire window. Here's everything you need to know about diagnosing seal failure and what it costs to fix in Toronto in 2026. What Is a Window Seal and Why Does It Fail? Modern windows are double-pane or triple-pane units — two or three sheets of glass with a sealed air or argon gas space between them. This sealed unit (called an IGU — Insulated Glass Unit) is what gives your window its insulating power. The seal around the IGU is made of rubber and a desiccant material that absorbs moisture. Over time — typically 15 to 25 years — this seal degrades due to: - Repeated expansion and contraction from Toronto's extreme temperature swings (-25°C winters to +35°C summers) - UV exposure breaking down the rubber seal - Water pooling on window sills and working into the frame - Age and normal wear South-facing windows typically fail sooner because they receive more UV and experience more dramatic temperature cycling throughout the day. How to Tell If Your Seal Has Failed The clearest sign is condensation or fogging between the panes — visible from inside but impossible to reach or wipe away. Other signs include: - A rainbow or oily haze effect on the glass - White mineral deposits or streaks between the panes - The glass looks dirty even after cleaning - Noticeably more cold drafts near that window One simple test: press gently on the centre of the glass pane. If you see the fog shift or move slightly, the seal has failed and moisture is trapped inside. Do You Need to Replace the Entire Window? In most cases, no. If your window frame is structurally sound — no rot, no warping, no broken hardware — you only need to replace the glass unit itself. This is called an IGU replacement and it's far more affordable than a full window replacement. What It Costs to Fix in Toronto in 2026 IGU (glass unit) replacement only: $150 to $350 per window Full window seal repair: $200 to $400 per window Window defogging service: $100 to $200 per window Full window replacement (if frame is damaged): $800 to $1,500 per window IGU replacement saves you 60 to 80 percent compared to replacing the full window. For most Toronto homes with standard-sized windows, fixing a failed seal costs under $300 per window. What Happens If You Ignore It? A failed seal doesn't immediately cause structural damage, but it does mean: - Your window has lost most of its insulating value — the gas between the panes is gone - Your heating and cooling bills increase, sometimes by 15 to 20 percent per window - Moisture trapped between panes can eventually cause mould growth in the frame - The longer you wait, the higher the risk of the glass itself cracking from thermal stress Is Seal Failure Covered by Home Insurance? In most cases, no. Window seal failure caused by normal wear and tear is not covered under standard Ontario home insurance policies. However, if the seal failed as a result of storm damage, a covered impact, or vandalism, your insurer may cover the repair minus your deductible. Get a Free Assessment At Window Fix GTA, we inspect seal failures across Brampton, Mississauga, Toronto, and the surrounding GTA — often same day. Our technicians will tell you honestly whether you need an IGU replacement or a full window replacement, and provide a transparent quote with no pressure. Call us at (647) 961-8637 or request a free quote online.