How to Seal Drafty Windows

If you can feel cold air near your windows in winter, heated air is escaping and your energy bills are probably higher than they need to be. Sealing those gaps is an inexpensive weekend job that also makes rooms feel noticeably more comfortable.

Find Where the Air Gets In

On a cool, windy day, move your hand slowly around the window frame, sash, and trim. A lit incense stick also works: watch for smoke that wavers or blows sideways. Keep any flame well away from curtains and blinds. You can also close the window on a strip of paper; if it slides out easily, the seal there is weak. Common leak points include:

• Gaps between the interior trim and the wall
• The joint where the two sashes meet on double-hung windows
• Worn or missing weatherstripping along moving parts
• Cracked or shrunken exterior caulk

Caulk the Gaps That Don’t Move

Use caulk on stationary joints, such as where trim meets the wall or where the exterior frame meets siding.

1. Scrape away old, cracked caulk and wipe the area clean and dry.
2. Choose paintable acrylic latex caulk for indoor trim, or an exterior-grade caulk for outside.
3. Cut the nozzle small and run a steady bead along the gap.
4. Smooth it with a damp finger and wipe up the excess.
5. Let it cure fully before painting over it.

Exterior caulk usually goes on best in mild, dry weather, so check the temperature range on the tube.

Weatherstrip the Moving Parts

Weatherstripping seals the parts of a window that open and close. Common types include:

• Self-adhesive foam tape: easy to apply and good for irregular gaps.
• V-strip or tension seal: fits along the sides of sliding sashes.
• Rubber or vinyl tubular gaskets: durable options for larger gaps.

1. Clean the surface with rubbing alcohol and let it dry.
2. Measure and cut the strips to length.
3. Press the strip firmly in place, keeping it straight.
4. Close the window to make sure it shuts and locks without forcing.

If the window is hard to close after you add weatherstripping, the strip is too thick for that gap. Swap it for a thinner profile rather than forcing the sash, which can damage the frame or the lock over time.

Quick Fixes for the Cold Months

• Window insulation film kits attach with double-sided tape and shrink tight with a hair dryer.
• Removable rope caulk presses into gaps and peels off in spring.
• Heavy curtains or cellular shades add another insulating layer.
• A draft stopper along the sill blocks air at the bottom.

Final Tips

• Don’t seal the small weep holes at the bottom of exterior window frames. They let water drain out.
• Never seal shut a window you rely on as an emergency exit.
• Inspect seals each fall before the weather turns.
• If frames are rotting or there’s fog trapped between the panes, a window repair professional may be the better call.