Failed window seal (thermos descellé): what it is, how serious, what it costs

A modern window has a sealed unit: two or three panes with dry air or gas between them, closed by an airtight seal. In Quebec, people call it a « thermos », and a French report will say « thermos descellé » when the seal has failed. Humid air then gets between the panes, and you see fog, streaks or a white haze inside the glass that cannot be wiped from either side.

The inspector only sees it when the weather and light allow: there may be more than the ones listed.

No, it is not serious. The window insulates a little less and the view is blurred, but there is no risk to the structure or to safety. In analyses, I almost always put it under “Can wait”.

What matters is how many: one or two sealed units are easy to replace. If there are many and the frames are worn, the windows themselves may be reaching the end of their life.

When the frame is in good shape, you replace only the sealed unit, not the window: $250 to $500 for one window, $700 to $1,600 for several windows on one side of the house. If the frames are done, replacing the windows on one side is more like $3,000 to $7,000.

These are ballpark figures for Quebec, to be confirmed with quotes.

1. How many sealed units have failed, and which ones?
2. What shape are the window frames and hardware in?
3. Do you know how old the windows are?

Ask the seller for the window invoices: some manufacturers warrant the sealed unit for several years.

Does your report mention failed window seals? Upload it: in five minutes, I tell you what comes first, what to have checked and what to ask the seller.

Some companies offer to defog the unit, but the seal stays broken. Replacing the sealed unit is the lasting fix.

A little: the insulating gas has escaped. The effect on heating stays modest; it is mostly the view that suffers.