Most windows since the 1980s are insulated glass units (IGUs), two (or three) panes of glass sealed together with an insulating gas (argon) and a spacer bar between them. The seal keeps the gas in and moisture out. When that seal fails, the unit loses its insulating value and moisture gets trapped between the panes. The whole sealed unit, not the frame, then needs replacing.
$600 to $1,200 per window installed in the GTA (range $400 to $2,000); whole-house is five figuresAddress soonWindows
The quick answer
A failed window seal shows as permanent fog or haze between the panes that won't wipe off, the insulating gas is gone, so it's a comfort and energy issue. One or two blown units is a small negotiation chip; failures across the house mean the windows are near end of life. Replacement runs about $600 to $1,200 per window in the GTA. Check the date stamped on the spacer bar to date the glass.
You are reading the failed window seals & sealed-unit age page. Type the year the house was built and I will tell you what else tends to be true at that age, what it costs, and what to ask. One number, ten seconds.
Free. No account. Educational and impartial, not a home inspection.
Why it matters
A failed seal means higher energy bills, cold drafts, and permanent fogging you can't clean off (it's between the glass). One or two blown units is a minor budget item and an easy negotiation chip; failed seals across the whole house signal the windows are near end of life, a real five-figure replacement. Single-pane windows (older homes) are a comfort and energy issue in the Canadian climate even before any seal question.
How to spot it
Look between the panes, not at the surface: haze, cloudiness, condensation, or a milky film that won't wipe away = a blown seal. Then date the unit: most IGUs carry a manufacture date stamped on the metal spacer bar visible between the panes, or etched in a corner of the glass (often a number/letter code or a month-year). That date tells you how old the glass is, regardless of how new the house or frames look, a key, easily-missed clue. Also check for rotted/soft wood sills, painted-shut or stuck sashes, and original aluminum frames (thermally poor, often sweat and ice up in winter).
What it costs
Toronto/GTA installed pricing runs $600 to $1,200 per window for mid-range vinyl (full market range $400 to $2,000; GTA prices 10 to 20% above the rest of Ontario). Replacing just the sealed glass unit (IGU) in a sound frame costs much less than a full-frame replacement, worth asking. A whole-house replacement is a real five-figure project.
What to do
Budget soon / negotiate. Count the foggy units, note the spacer-bar date stamp where you can read it, and get a glazier or window company to quote. A few blown seals = a small ask in your offer; many + an old date stamp = factor a replacement into your number.
Education and triage, not a home inspection. Casaroo flags fogging and dates the glass from what you can see, a glazier confirms whether it's a sealed-unit swap or a full window replacement.
Common questions
Can I replace just the glass instead of the whole window?
Often yes, and it is worth asking. Replacing the sealed unit in a sound frame costs considerably less than a full-frame replacement, which runs $600 to $1,200 per window in the GTA.
How do I tell how old the glass is?
Most sealed units carry a manufacture date stamped on the metal spacer bar between the panes, or etched in a corner of the glass. That date tells you the age of the glass regardless of how new the house or the frames look, and it is one of the most useful clues buyers never check.
Is one foggy window worth negotiating over?
One or two is a small ask that usually gets folded into a larger list. Failed seals across the whole house are a different conversation, because that signals the windows are near end of life and you are looking at a five-figure replacement.
Does a foggy window mean the house has a moisture problem?
No. A blown seal is a failure of the window unit itself, not a sign of humidity in the house. Condensation on the inside surface of the glass in winter is a different finding, and that one is worth asking about.
Industry/glazier guidance on insulated glass unit (IGU) seal failure and the spacer-bar date stamp. Casaroo flags, it does not inspect; confirm scope with a licensed window/glass professional.
Last reviewed 2026-07-10.
This guide is general education, not a home inspection and not advice for your specific property. Always
consult the appropriate licensed professional, and get a licensed home inspection before you remove conditions
or buy. Cost ranges are 2026 estimates that vary by region, size, and access; confirm specifics with a
qualified professional.