Why Is There Fog Between My Window Panes?
by the Berry team · Updated
Fog or moisture trapped between the panes of a double-pane window means the seal around the glass has failed, letting humid air into the space that is supposed to be sealed. It is not an emergency, but the haze will not go away on its own, and the usual fix is replacing the sealed glass unit rather than the whole window.
Your options and what they cost
Prices are per window for common residential sizes. Large, custom, tempered, or specialty glass costs more.
| Option | What it does | DIY cost | Pro cost |
|---|---|---|---|
| Leave it | Fine if the fog is light and you can live with the look. Insulation is somewhat reduced. | DIY$0 | ProNo cost |
| Warranty claim | Many window makers warranty the glass seal for years. Find the brand and date etched on a corner of the glass. | DIY$0 to file | ProGlass often covered, labor sometimes extra |
| Replace the glass unit only | A new sealed glass unit goes into the existing frame. The most common fix. | DIYNot recommended | Pro$150-$600 per window |
| Defogging service | Drills small holes, cleans and dries the space, and seals the holes. Improves the look, does not restore the original seal or gas fill. | DIYNot recommended | Pro$75-$150 per window |
| Replace the whole window | Makes sense when frames are rotting, warped, or drafty, or several windows are failing. | DIYNot recommended | Pro$500-$1,500+ per window installed |
Ranges are typical US prices and vary with your region, your home, and the season. A pro quote for your exact job beats any range.
Is it the seal or just condensation?
Wipe the inside surface. If the moisture wipes off from inside the room, it is indoor humidity condensing on cold glass, not a failed seal.
Wipe the outside surface. Dew on the outside of the glass on cool mornings is normal, especially on efficient windows. It burns off as the sun hits it.
Nothing wipes off. If the haze, droplets, or white mineral streaks are between the panes, the seal has failed.
If you see a lot of condensation on the inside of many windows in winter, the issue is usually indoor humidity. Running bath and kitchen fans, and keeping indoor humidity moderate in cold weather, helps.
Why seals fail
A double-pane window is two sheets of glass with a sealed spacer around the edge. The space between them is often filled with argon or another insulating gas. Every day the glass heats and cools, the seal flexes a little. Over years, the seal can break down, especially on windows that get strong afternoon sun, sit in a frame that holds water, or were made poorly. Once air gets in, it brings moisture, which condenses between the panes and leaves mineral spots as it dries.
Does it matter?
Mostly it is a view and resale problem. A failed seal means the insulating gas has leaked out, so the window insulates somewhat less, but it is still two panes of glass. It does not let water into the house and does not make the window unsafe. Fixing one foggy window is rarely worth it for energy savings alone.
The exception is water. If you also see moisture on the sill, peeling paint, or soft wood around the frame, water is getting into the window itself, and that is worth fixing soon. See siding repair costs if the damage extends into the wall around it.
Glass only or the whole window?
Replace just the glass unit if the frame and sash are in good shape and only one or two windows are fogged. It is cheaper, faster, and does not disturb trim or siding.
Consider full window replacement if the frames are rotting or warped, the windows are drafty or hard to operate, or many of them are failing at once. At that point, paying for glass in old frames often means paying twice.
When to call a pro
- One or more windows have fog, droplets, or streaks between the panes that you want gone.
- You see rot, soft wood, or peeling paint around a window frame or sill.
- Glass is cracked, or the window is hard to open, close, or lock.
- Several windows are failing and you want to compare glass replacement to full replacement.
What makes it worse if you wait
- Moisture between the panes leaves mineral deposits that etch the glass, so the haze gets harder to see through over time.
- If the frame around a failing window is also letting in water, that rot spreads into the sill and the wall framing.
- Warranty periods run out. If the windows are still under warranty, filing sooner is better.
Common questions
Can you fix a foggy double-pane window?
Yes. The common fix is replacing the sealed glass unit, which typically costs $150-$600 per window. Defogging services can clean the haze for less, but they do not restore the original seal or insulating gas.
Is a foggy window an energy problem?
Somewhat. The insulating gas has leaked out, so the window insulates a little less, but it is still double glass. For one or two windows, the energy loss is usually small. The bigger issues are appearance and resale.
Is fog between window panes covered by warranty?
Often. Many window manufacturers warranty the glass seal for years, sometimes for as long as you own the home. Look for a brand name and date code on a corner of the glass, then check with the manufacturer.
Why do my windows have condensation on the inside?
Moisture you can wipe off from inside the room is indoor humidity condensing on cold glass, not a failed seal. Running bath and kitchen exhaust fans and keeping indoor humidity moderate in winter usually helps.
Not sure that's your problem? Snap a photo and Berry will tell you what it is and what it should cost.
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