What Does a Foggy Window Mean?
A foggy window is a sealed insulated glass unit that has lost its seal. When it was made, the space between the two panes was filled with dry Argon gas and sealed shut. A strip of desiccant inside the spacer soaked up any leftover moisture. When the edge seal fails, humid outdoor air gets in, the desiccant fills up, and water condenses on the inside of the glass as fog, droplets or a milky haze.
Fog that comes and goes with the weather is the early stage. A permanent white haze or streaky mineral deposits mean the unit has been wet for a long time and the glass surfaces are now stained. Either way, the unit cannot be dried out and resealed in a way that lasts.
Why Sealed Units Fail
Most seal failures come from one or more of these:
- Age. A good dual-seal unit lasts 20 years or more. Builder-grade single-seal units from the 1990s and 2000s often fail in 10-15.
- Thermal pumping. Sun heats the gas, it expands, night cools it, it contracts. Thousands of cycles work the seal loose.
- Water sitting on the seal. Blocked weep holes or a sash that holds water against the bottom edge break down the seal from outside.
- Bad installation. Units set without setting blocks, or with the seal crushed, fail early.
Foggy Window Repair Options Compared
| Option | Cost per window | Fixes the view | Restores insulation | Warranty |
|---|---|---|---|---|
| Drill-and-vent defogging | Lower | Temporarily | No | Short or none |
| New sealed unit in existing sash | $350-$680 | Yes | Yes | 10-year seal + 2-year workmanship |
| Full new window | $3,800-$4,500 | Yes | Yes | Varies by maker |
For a window with a sound frame, a new sealed unit is the best value by a wide margin. That is the only option we offer, because it is the only one we can stand behind in writing.
What We Check While We Are There
A foggy window is often a sign of water where it should not be. While measuring, the crew checks the sill and sash for soft wood or swollen MDF, looks at weep holes on sliders and casements, and checks for gaps in exterior caulking. If water is getting in, we tell you and fix the cause when we install, so the new unit does not suffer the same fate.
Do the Worst Windows First
You do not have to replace every foggy window at once. We quote each unit separately, with sizes and prices on one page, so you can do the bedrooms or the street-facing windows now and the rest next year. The units are made to measure, so ordering them in batches costs the same per window.
Have a few foggy windows? Snap a photo of each one and send us a message. Our Toronto glass repair crew will tell you which are worth doing now.
Written by The Elite Glass Repair Toronto Crew. Last updated .
