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🍁 Built for Canadian homes — written to Canadian codes and provincial rules. Not intended for use outside Canada.
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Foggy or cloudy double-pane window (moisture between the panes)

A window that's gone cloudy is annoying to look through, but a fogged sealed unit is a cosmetic and efficiency problem — not a safety one — and there's no rush to fix it.

tuneWhat are you noticing?
Select anything that matches and the checklist below reorders to fit. Not sure? Skip it.
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In Canadian homes, the tell is that the haze won't wipe off. Wipe both the inside and the outside faces of the glass: if the cloudiness, droplets, or a milky film stays put no matter which side you clean, the moisture is sealed BETWEEN the panes and the insulated glass unit's seal has failed. That's a glazing fix — the sealed glass unit (or the whole sash) is replaced while the frame stays — and no amount of dehumidifying will clear it.

Ranked from real-world failure data. The order updates as you select what you’re noticing above.

Likely causes, in the order to check them

Showing the typical order
Beginner-friendly Doable, with care Safety-critical Call a pro

visibilityHow to check

  1. Wipe the inside face of the glass with a dry cloth. If the fog wipes clean, it's surface condensation from indoor humidity — work that instead (see the windows condensation page); it isn't a seal failure.
  2. Wipe the outside face too. On a cool morning, dew or light frost sits out there on an efficient window and clears as the day warms — also not a seal failure.
  3. If a haze, droplets, mineral streaks, or a milky film stays put no matter which face you wipe — often worst in the middle of the pane — the moisture is sealed BETWEEN the panes. That confirms a failed insulated glass unit in that window.
  4. Note which windows are affected and roughly measure each pane (width, height, and the glass thickness/spacer if you can see the edge). A glass shop will need those numbers, and it tells you the scope before you call.
buildNo tools schedule5 min

handymanHow to fix it

warning Large glass is heavy and sharp — know when to hand it offA sealed glass unit is a heavy slab of glass with sharp edges, and getting the measurement, setting blocks, and re-seal right is what keeps the new unit from fogging next winter. Swapping a small, accessible, stopped-in unit at ground level is a reasonable careful-DIY job with gloves and a helper. Anything large, high up, on an upper floor, or held in with structural glazing tape belongs to a glass shop — they do this every day, usually for a few hundred dollars per window, and the frame stays put. There's no urgency: a fogged unit is cosmetic, not a safety issue.

Have the sealed glass unit measured and replaced — the frame and sash usually stay. A glass shop can re-glaze in place or take just the sash; a careful DIYer can swap an accessible, stopped-in unit. Until then the fog is only cosmetic and slightly less efficient, so there's no rush.

  1. Measure the sealed unit carefully — width, height, overall thickness, and pane count — or, easier and safer, remove the sash and take the whole thing to a glass shop to measure and match (including any low-e coating and argon fill).
  2. Order the replacement sealed unit. This is the part with the lead time; the window stays usable and only cosmetically fogged while you wait.
  3. If you're doing it yourself on a stopped-in unit: pry off the glazing stops or beads carefully, note their order, and lift the old unit out onto a padded surface — sealed units are heavy and the edges are sharp.
  4. Set the new unit on the same setting blocks, re-fit the stops, and seal per the manufacturer's instructions. If the unit is large, high up, or held in with structural glazing tape, stop and let a glass shop do it — it's a routine job for them.
schedule120 min savings$120–400
Replacement insulated glass unit (sealed unit)Match width, height, overall thickness, pane count, any low-e coating, and gas fill; a glass shop will size it from the old unit or the sash
gavel Check your province first AB: homeowner may do this · BC: homeowner may do this · ON: homeowner may do this · PE: homeowner may do this · QC: homeowner may do this
Replacing a sealed glass unit (the glass only, frame in place) is homeowner-or-contractor work across Canada. Note separately: replacing the whole window, changing the opening size, or a bedroom egress window may require a building permit and a contractor — verify the municipal/provincial rule before that scope of work.

handymanHow to fix it

This isn't a window to replace — it's indoor humidity to manage. Wipe the glass to confirm it clears, then lower indoor humidity: run bath and kitchen fans, turn a furnace humidifier down in cold weather, and re-check with a hygrometer. See the windows condensation page for the full humidity ladder.

  1. Confirm it's surface condensation: wipe the inside glass and watch it clear. If it clears, no seal has failed — this is a humidity issue.
  2. Run bath fans during and after showers and the range hood when cooking, and turn any furnace humidifier down during cold snaps.
  3. Check indoor humidity with a hygrometer and bring it down toward the cold-weather target; the windows condensation page has the outdoor-temperature-vs-humidity guide.
schedule20 min savings$0–20
gavel Check your province first AB: homeowner may do this · BC: homeowner may do this · ON: homeowner may do this · PE: homeowner may do this · QC: homeowner may do this
Managing indoor humidity — running fans, adjusting a humidifier, using a hygrometer — is routine homeowner maintenance in every province.
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Why the list is in this order

We don’t sort by likelihood alone. We sort the way a good, honest tradesperson thinks: rule out the free, safe, common causes first. That’s why the cheap checks outrank the expensive repairs — and why anything dangerous gets a hard stop instead of a pep talk. The order exists to save you money, not to sell you anything.