Not all “foggy windows” are the same job. One kind is a failed window. The other is your house telling you it is damp.
Fog between the panes
Look at the glass from an angle. If the haze, mineral dots, or film sit inside the two panes — where a cloth cannot reach — the insulated glass unit has lost its seal.
That seal is what holds the dry air or argon between the panes. Once it fails:
- The view stays cloudy
- The unit loses most of its insulating value
- The fog can come and go with the weather, then settle in
This is common on older double-pane units after years of sun, movement, and Washington wet-dry cycling.
Moisture on the room side
If you can wipe the water off the inside of the glass, the window may still be doing its job. Warm indoor air hit cold glass and dropped its water there. Showers, cooking, and a house that does not vent well make it worse, especially on single-pane or metal-frame windows.
That is a humidity and glass-temperature problem. Better fans help. A tighter, warmer replacement unit also helps because the indoor face of the glass stays closer to room temperature.
What replacement changes
A new insulated unit with a sound spacer and a tight frame does two different things:
- It removes the failed, cloudy glass
- It raises the inside glass temperature so everyday winter condensation is less likely
It will not fix a crawl space that pumps moisture or a bath fan that does not reach outside. We will say so if that is what we see.
Why Washington accelerates this
A sealed unit’s spacer and desiccant are rated for a service life, not forever. Two things in this climate use that life up faster than average:
- Wet-dry cycling. Nine wet months and three dry ones put more stress on the seal than a steady climate does — it expands and contracts with every swing.
- West and south sun exposure. UV and heat break down the sealant faster on unshaded elevations, which is why one side of a house often fogs first.
None of that means every unit fails on a schedule. A shaded, north-facing window can outlast a sun-battered one by a decade or more.
A simple check before you call
- Try to wipe the haze. If it does not move, the unit has failed.
- Note how many openings look like that.
- Check the sill for soft wood. Failed glass plus a wet sill is a full-frame conversation.
Bring those notes to an estimate. We will tell you which units are done and which can wait.
Common questions
Can fog between the panes be repaired?
Some shops drill and defog. That can clear the view for a while. It does not restore the insulating gas or a reliable seal. For a window you plan to keep, replacement of the glass unit or the whole window is the lasting fix.
Why do my windows sweat in winter but look clear in summer?
That is usually room-side condensation. Indoor air is wetter than the cold glass. Bath fans, a tighter house, and warmer glass all help. It is not automatically a failed window.
Does fogged glass mean I need every window replaced?
Only the failed units are required. We often replace a few now and plan the rest of the house as a second trip.