If the haze stays put after you wipe both sides of the glass, it's inside the sealed unit, and the seal around that unit has let go. Nothing you spray, heat or drill will make that seal whole again. It's seldom urgent. Your two lasting options are a fresh glass unit in a healthy frame, or a replacement window: about $450-$1,800 installed around Portland, typically near $825, unit and materials included (market data, November 2026) .
Why does a double-pane window fog up between the glass?
A double-pane unit is two sheets of glass held apart by a metal or plastic spacer around the edge. A bead of sealant closes the gap, and the spacer is packed with a drying agent (desiccant) that soaks up the little moisture trapped at the factory. Sun swells the air in that gap every afternoon and cold shrinks it every night, and over years that push and pull works the sealant loose.
Once the edge leaks, damp air drifts in, the desiccant fills up, and water condenses on the inner faces of the glass. Later you often get a white film or streaks that stay on dry days too, because minerals have dried onto the glass. A broken window seal doesn't heal. Our wet, mild winters keep the outside air damp for months, so a leaking unit on a west-side house never runs short of moisture to pull in.
Is the fog between the panes, on the room side, or outside?
Take a dry cloth to the room side first; if the glass clears, you're looking at indoor humidity, not a seal. Then go outside and wipe there. Dew on the outer pane on a cool morning is fine, since it means the inner pane is keeping the house's warmth from reaching it. If neither cloth touches the haze, the seal has failed.
Room-side condensation is common here in winter, when houses stay shut and showers, cooking and laundry on a drying rack all add water to the air. The lowest corners of the glass run coldest, so they fog first. Run the bath fan and range hood longer, crack a window for a few minutes, or use a dehumidifier. When the bathroom fan barely pulls or there isn't one, a new exhaust fan is often the real cure.
Water that runs down the inside of the glass every morning soaks into the sill and the lower rail of the sash, and that's how sill rot gets going .
Can you get the moisture out of a sealed window? Does a hair dryer work?
A hair dryer or a warm afternoon may thin the fog for a few hours. It's back after the next cold night, because the seal is still open.
Defogging services and kits drill a small hole in one pane, wash and dry the space, and fit a vent or a plug. That can clear the view. It doesn't reseal the unit, and it doesn't put back any insulating gas the unit held, if it had any; some units only ever held plain air. Mineral etching that has already set into the glass may never wash out.
One hard rule: never drill tempered glass, because it shatters. Glass in doors and sidelights, near tubs and showers, and in big low panes is usually tempered, and a tempered pane carries a small etched stamp in one corner. We don't defog windows .
Is a foggy double pane a problem, or only an eyesore?
Mostly a nuisance you can plan around. The window still keeps rain out and still opens; you lose the clear view and some of that unit's insulating value. It turns urgent only when water is also getting into the wood, so press on the sill and the lower sash and look for dark, soft spots or lifting paint.
Buyers see "failed seals" on inspection reports all the time; our guide to repairs after a home inspection covers how to sort that list. Before you ask for a quote, count every fogged unit in the house. Then look along the spacer bar or in a glass corner for a maker's name or a date. Some makers cover seal failure under their own warranty, so check with them first.
Should you replace just the glass, the sash, or the whole window?
- A new sealed glass unit. A glass shop measures the old unit, orders one to size and sets it into your existing sash or frame. It fits when the frame and sash are sound and only one or two units have fogged. This is usually glass-shop work .
- A new sash. Some window makers sell a replacement sash for their own models; you need the make and model to order one .
- A new window. Go this way when several units have fogged, the frame is cracked or rotted, the window is single glazing or bare aluminum that drips every winter, or nobody makes the parts anymore. Around Portland that's $450-$1,800 a window, about $825 in the middle, unit included (market data, November 2026) . For whole-house counts and frame choices, see what window replacement costs.
On Oregon's Building Codes Division list of exempt work, a window swap with no structural change needs no permit; cutting a new opening or resizing one does. Portland's guidance adds that new glass in hazardous spots, such as beside doors, tubs and showers, has to be tested, labelled safety glass, replacements included. Keep that in mind for a fogged sidelight.
Repair or replace: what about rotted sills and stuck sashes?
Fog is rarely the only thing wrong with an older window. Here's how we'd sort it, one window at a time.
| What you see | Usual answer | Portland-area range | Basis |
|---|---|---|---|
| Fog in one or two units, frame sound | New glass unit (glass shop) | no figure | - |
| Fog in most units, or a frame cracked or soft through | New window | $450-$1,800 each (about $825) | with materials |
| Sash sticks or won't stay up; lock or crank broken | Fix the balance, lock or crank | $150-$600 (about $300) | labour only |
| Soft spot on the sill or lower frame | Epoxy, or patch in new sill wood | $300-$1,200 (about $600) | labour only |
| Rot running into trim, siding or framing below | Larger rot repair | $500-$4,000 (about $1,500) | with materials |
| Cracked or loose casing, water stains on trim | Trim and casing repair | $200-$800 (about $400) | labour only |
| Drafts or gaps at the frame edge | Re-caulk and seal | $150-$800 (about $350) | labour only |
These are what the Portland-area market charged as of November 2026; they aren't quotes from us .
The rule of thumb is simple. If one part failed, fix that part through window repair. If the whole unit failed, or three things went wrong on the same window, replace it. A sticky vinyl or aluminum slider is often just grit in the track and worn rollers, not a dead window .
Rain sitting on flat sills is what softens them on west-side houses. Once the soft wood spreads past the sill, it's wood rot repair, and drafts at the frame edge are a sealing and draft-proofing job. Most Bethany homes went up in the 1990s and 2000s, so their builder windows have had a quarter century or more of sun, about when fog starts showing in more than one room. Over in Cedar Hills, plenty of 1950s-60s tract houses keep the windows they were built with.
How long should double-pane windows last before the seals go?
There's no honest single number. Hard sun on south and west walls, water sitting along the lower edge of the glass and a sash that gets slammed all shorten it, and age by itself doesn't justify replacing a window that's clear and works .
What if the house dates from before 1978?
Then the year matters whichever way you go. Oregon assumes a pre-1978 home has lead paint until testing proves it doesn't. The Oregon Health Authority lists window repair and window replacement among covered renovation activities, and Oregon guidance treats window replacement as renovation. The federal allowance for small jobs (under 6 sq ft inside or 20 sq ft outside) doesn't apply once a window is being replaced. So scraping and repairing an old painted sash disturbs paint, and so does pulling the whole window. That's our reading, not legal advice.
Lead-based paint work isn't on our list ; it sits with the rest of the work we turn down, and our Oregon lead paint guide has the detail. Most houses in Cedar Hills or Cedar Mill went up before 1978. Bethany's didn't.