How to Seal Drafty Windows
Published October 15, 2025 · Updated March 1, 2026
Drafty windows can account for 25-30% of heating and cooling energy loss in an average home. Sealing them with weatherstripping and caulk is the most cost-effective energy efficiency improvement available — materials cost under $30 and the savings show up immediately on your energy bill.
What You'll Need
🛠 Tools
📦 Materials
Safety First
- •Work in temperatures above 45°F — caulk doesn't cure properly in cold weather.
Step-by-Step Instructions
Find the Drafts
On a cold, windy day, hold a lit stick of incense slowly along the window perimeter. Smoke that flickers or bends identifies drafts. Check the gap between moving sash and the frame, around the window frame and wall junction, and near hardware. Mark problem areas with painter's tape.
A damp hand is even more sensitive than incense — evaporative cooling makes even small drafts very noticeable.
Seal Sash Gaps with Weatherstripping
The most common draft location is where the window sash (movable part) meets the window frame. Clean the sash channel with a dry cloth. Cut V-strip weatherstripping to length (measure and cut to fit each channel). Peel the backing from self-adhesive V-strip and press firmly into the channel where the sash contacts the frame.
V-strip (spring bronze or rigid plastic) outlasts foam tape by 5-10 years. It costs slightly more and requires more careful installation, but it's worth it for frequently used windows.
Apply Foam Tape to Sash Contact Points
For the horizontal contact points (top and bottom of the sash where it meets the sill and top rail), apply self-adhesive foam tape. Choose thickness carefully — the tape should be slightly compressed when the window closes, not squashed flat or leaving a gap.
Remove and Replace Old Caulk
Use a utility knife to score along the edge of old caulk around the window frame, then a stiff scraper or putty knife to remove it. Old cracked caulk is worse than no caulk — it channels water into the gap instead of deflecting it. Clean the surface and let dry.
New caulk applied over old, deteriorated caulk won't adhere well and will fail again within one season. Always remove old material first.
Caulk the Frame-to-Wall Gap
Cut the caulk tube tip at 45° to match the gap width. Apply a continuous bead of caulk along the gap between the window frame and the wall, from the outside (use exterior-grade silicone or polyurethane caulk) and from the inside (use paintable interior latex caulk). Smooth with a wet finger or caulk tool and wipe up any excess immediately.
Apply Rope Caulk for Seasonal Sealing
For windows you won't open in winter, press rope caulk (a non-hardening putty sold in coils) into any remaining gaps around the sash from the interior side. It provides excellent sealing, remains flexible throughout the heating season, and pulls off cleanly in spring without damaging paint.
Check Locks and Latches
A window that doesn't fully latch creates a persistent air gap. Test each lock: it should engage completely and draw the sash firmly against the weatherstripping. Lubricate stiff locks with graphite powder. Bent or broken latches can often be straightened or replaced for a few dollars.
Test and Verify
Repeat the incense or damp-hand test after sealing to verify you've caught all drafts. Check your first energy bill after sealing — the savings on a drafty older house can be $30-60 per month in winter. Also check around the window on cold days for condensation, which indicates remaining air leaks.
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