What it usually means, the likely causes in order, what to safely try first, what a pro charges in Canada, and when to stop and call one.
This guide covers the common cases. Describe your exact problem and get a personalized diagnosis — free to start, with a DIY vs. call-a-pro verdict and a real cost estimate.
Foggy glass between the panes and a cracked pane look like cousins but are different faults. Fog that appears inside a double-pane unit, often clearing and returning with the weather, is a failed seal: the insulating unit has lost its sealed, dry interior, and moist air now condenses on the inner surfaces where no cloth can reach. A crack is physical damage to one pane, from impact, stress, or a frame that has moved. In both cases the frame and hardware are usually innocent, and the fix is about the glass unit itself, which is why cleaning, inside and out, never changes foggy glass no matter how thoroughly it is done.
Neither problem is an emergency in most cases, but neither heals. A failed seal will keep fogging and slowly lose insulating value, so replacement is a planned job for the coming weeks or months. A crack deserves faster attention if it is spreading, if the pane is in a door or low window where breakage risk matters, if weather can reach the opening, or if the damaged unit is the only barrier in an exterior wall. Tape a weather-exposed crack and book the glass work rather than watching it through a season of storms.
Double-pane units are sealed at the factory with dry air or gas between the panes. Years of sun heating one side, daily expansion and contraction, and age degrade that perimeter seal until moist air works in and condenses where it cannot be wiped. South and west units, baked by sun, commonly fail first, which is why one window fogs years before its shaded neighbour.
A stone from a mower, a ball, a bird strike, or a tool during other work cracks a pane in the familiar star or radiating pattern centred on the impact point. Only the struck pane usually breaks, leaving the other pane and the frame intact, which matters because the repair scope is the glass unit, not the window.
Glass can crack without anything hitting it: strong temperature differences across a partly shaded pane, a frame that has racked and pinches a corner, or a door slammed hard against a binding frame. Stress cracks typically start at an edge or corner and run in a single sweeping line, unlike the centred pattern of an impact.
Older insulating units simply reach the end of their seal life across a house at similar times, so several windows fogging within a year or two of each other is common in homes of a certain age. That pattern changes the planning conversation from one unit to a staged replacement of the worst units first.
| Job size | Typical estimate (CAD) |
|---|---|
| Simple fix — the straightforward version of this repair | $100–$300 |
| Major job — complex, hidden, or replacement-level work | $300–$900 |
Estimates only, calibrated to Greater Toronto Area trade rates and adjusted by region on this site — not a quote. Your exact price depends on the cause, parts, and access. A personalized diagnosis narrows this range using your specific symptom.
Measuring, photographing, and temporary taping are homeowner tasks. The replacement itself is normally professional work: the insulating unit is custom-made to size, the old unit must come out without damaging the sash, and the new one must be set, shimmed, and sealed correctly or its seal life starts compromised. On older windows with a rotted or warped frame, get an honest comparison between a new glass unit and replacing the window, because good glass in a dying frame is rarely the right spend. Defogging services exist but results vary; ask what guarantee, if any, stands behind them.
The fog is moisture and mineral residue on the inner surfaces of a sealed unit, so no cleaning from the room can reach it. Some services drill and vent units to clear the moisture, with mixed and often temporary results, since the seal has still failed. The durable fix is a new sealed glass unit fitted into your existing frame and sash, which restores the insulation and the view without replacing the whole window.
Usually not. In most modern windows the insulating glass unit is replaceable on its own, and the frame, sash, and hardware stay in place, which is substantially less work than a full window replacement. Replacement of the whole window enters the picture when the frame is rotted, warped, or itself obsolete. A glass professional can confirm which situation you have once they see the frame condition, so ask that question explicitly.
Because they were made and installed around the same time and have lived through the same sun and seasons. Seals age as a population, so a cluster of failures in a house of a certain age is expected rather than unlucky. It is worth surveying all your windows before ordering, then replacing the worst units first and planning the rest, rather than discovering the next failure one month at a time.
It is weakened, which is the point. A cracked pane has lost much of its strength and can fail completely under a slam, a temperature swing, or casual pressure that intact glass would shrug off, and the resulting edges are very sharp. Location decides urgency: a small crack high in a fixed window can wait for a booked repair, while any crack in a door, sidelight, or low window should be protected and prioritised.
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