Drafty & Foggy Windows: What You Can Fix

"My window's bad" can mean two very different things. One is a draft you can seal in an afternoon. The other is fog trapped between the glass, which is a failed sealed unit and not a DIY repair. Knowing which you've got saves you money and frustration.

Drafts: usually a DIY fix

If you feel cold air around a closed window, the air is sneaking past worn seals or gaps in the trim, not through the glass. You can usually knock it out yourself:

1. Find the leak. On a windy day, move your hand around the window, or hold a lit incense stick and watch the smoke pull toward the gap.
2. Re-caulk the exterior trim. Gaps where the window frame meets the siding are a common culprit. Pull old cracked caulk and lay a fresh exterior bead (see our caulking guide).
3. Add or replace weatherstripping on the sashes where they meet, so the moving parts seal when closed.
4. Use window film for winter. Shrink-to-fit interior film adds a cheap, effective air barrier on drafty single-pane windows for the cold months.

Fog between the panes: not a DIY fix

If your window looks foggy, cloudy, or has moisture between the two panes of glass that you can't wipe away, the seal on that insulated glass unit has failed. Modern double-pane windows have a sealed, sometimes gas-filled space between the panes; once that seal breaks, moisture gets in and the insulating value drops. There's no caulk or spray that reliably fixes this. The real solutions are replacing the insulated glass unit (the sealed glass "sandwich") or the window, which is glazing work, not a homeowner patch.

A note on condensation

Fog on the inside surface of your windows in winter is often a sign of high indoor humidity, not a window defect. Running bath and kitchen fans, and keeping humidity in check, usually clears it. Persistent heavy condensation, though, is worth understanding, since chronic moisture can lead to mold and rot around the window.

Know when to call a pro

Sealing drafts is great DIY. Call a pro when you've got foggy or moisture-filled glass (failed sealed unit), a rotted or soft window frame or sill, a window that won't stay open, won't lock, or won't close square, or persistent condensation with staining that suggests a moisture problem. Those are glazing and repair jobs, and catching a rotted sill early keeps it from spreading into the wall.