How to Winterize Old Wood Windows

Old wood windows have a reputation for being drafty, but most of the cold comes through a few gaps you can find and seal in an afternoon. Winterizing is mostly about two things: stopping air leaks and keeping water out of the wood.

Here's how to get older windows ready for a northern Illinois winter — in order, starting with the free steps.

1. Lock Every Window

A sash lock does more than keep the window closed: it pulls the two sashes together at the meeting rail and presses them against their seals. An unlocked double-hung window is almost always a drafty one. If a lock won't line up or catch, that's worth fixing before winter.

2. Find the Drafts

On a windy day, hold a lit candle or incense stick near the edges of each sash, the meeting rail and the joint between the frame and the wall. Where the smoke wavers, air is getting in. Note each spot — the fix depends on where the gap is.

3. Seal the Gaps You Found

• Sash seams: press removable rope caulk into the gaps around the sash. It peels off in spring without damaging paint.
• Worn weatherstripping: replacing flattened or missing weatherstripping stops drafts at the source. Some types are easy to replace; weatherstripping built into sash channels is best left to a pro.
• Frame-to-wall joints: cracked exterior caulk should be cut out and replaced in dry, mild weather, before the cold sets in.

Don't permanently caulk or paint operable windows shut. Bedroom windows are emergency exits, and sealing a window completely can trap moisture against the wood.

4. Close Up Your Storm Windows

Swap screen panels for glass, make sure every panel closes fully, and clear the small weep holes at the bottom of the storm frame so water can drain.

A working storm window adds a second layer of glass and a pocket of still air — one of the most effective upgrades for single-pane windows. Replace any cracked storm glass now, not in January.

5. Check Glazing and Sills Before the Freeze

Look at the glazing putty around each pane: cracked or missing putty lets water into the sash. Press a screwdriver into the sills and the bottom of each sash to find soft spots.

Glazing and paint need mild temperatures to cure, so these repairs belong in early fall — a soft spot fixed now is a small repair; left through winter, it spreads.

6. Add an Interior Layer if You Need One

Clear shrink-film kits applied inside the window frame add an insulating air layer for the season. Heavy curtains closed at night help too — and open them on sunny days to let the sun warm the room.

7. Keep Indoor Humidity Moderate

Heavy condensation on cold glass runs down onto the interior sill and soaks into the wood. Running bath and kitchen fans and avoiding over-humidifying keeps windows clear and sills dry. More in why windows fog up in Illinois winters.

What to Leave to a Pro

• Broken sash cords or balances — the sash is heavy and weights can fall inside the wall.
• Rotted sills or sash bottoms — filler over rot traps moisture.
• Reglazing large or upper-floor sashes.
• Stripping or sanding paint in homes built before 1978, which may contain lead.

If you find problems while winterizing, send us a photo — we'll tell you what needs fixing now and what can wait until spring.