Symptoms
- Feel moving air near the window edges
- Curtains move slightly on windy days
- Room near the window feels colder
- Higher heating bills in winter
Likely causes
- CommonWorn or missing weatherstrippingFoam or vinyl seals compress and crack after several years.
- CommonGaps between the frame and wallOld or shrunk caulk around the exterior trim lets air through.
- PossibleSash not closing fully or tightlyA loose lock or misaligned sash leaves a hairline gap.
- PossibleSingle-pane glass with no storm windowSingle glazing conducts cold regardless of sealing.
- PossibleGaps at the interior trim or sillOld caulk lines inside can shrink and separate.
What to do
- Feel around the sash and frame edges with a damp hand or a lit candle held near the seams (kept away from curtains) to find the draft's path.
- Check the weatherstripping for gaps, flattening, or missing sections along the sash channel.
- Peel off old weatherstripping and press in new self-adhesive foam or V-strip weatherstripping matched to the gap size.
- Inspect exterior caulk around the trim; scrape out cracked caulk and reapply a paintable exterior caulk.
- Tighten the sash lock so the two sashes pull snugly together, which closes most of the remaining gap.
- For a persistent draft with good weatherstripping, add a window insulation film kit or storm window for the winter.
- Recheck for drafts on a windy day after sealing to confirm the fix worked.
Tools and parts
- Caulk gun
- Utility knife
- Weatherstripping
- Exterior caulk
Self-adhesive foam weatherstrippingSearch: “window weatherstripping foam tape”
Exterior window caulkSearch: “paintable exterior window caulk”
When to call a pro
Call a window installer if drafts persist after resealing, which usually means the window itself is old or damaged enough to need replacement.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.