Knowing how to seal a window draft before winter is one of the highest-return DIY projects you can do. If you feel cold air near a window even when it’s closed, that’s money leaking out of your house every month — and fixing it costs almost nothing, takes an afternoon, and can noticeably reduce your heating bill.

Find the Draft First

Before you seal anything, find out exactly where air is getting in. Hold a lit stick of incense or a thin piece of tissue near the window edges on a windy day. If it flickers or gets pulled, you’ve found your leak. Common spots are the gap between the window frame and the wall, the seam between the upper and lower sashes, and around the lock hardware.

For Small Gaps — Weatherstripping

Weatherstripping is a foam or rubber strip that creates a seal where the window sash meets the frame. It peels-and-sticks directly onto the frame surface. Clean the surface with rubbing alcohol first so it adheres properly, cut to length, press firmly in place. A pack of weatherstripping costs about $8 and handles several windows. This is the right fix for drafts coming through the moving parts of the window.

For Gaps Around the Frame — Caulk

If air is coming in around the window frame itself (between the frame and the wall), caulk is your fix. Use a paintable latex caulk for interior use. Cut the tip of the tube at a 45-degree angle, apply a thin bead along the gap, and smooth with a wet finger. Let it dry for 24 hours before painting. Don’t use exterior caulk indoors — it stays rubbery and won’t paint cleanly.

For Really Bad Windows — Window Film

If the window itself is old and single-pane, the glass is losing heat even if the seals are perfect. A window insulation film kit (about $15 for several windows) adds a layer of clear plastic film over the entire window using double-sided tape. You shrink it tight with a hair dryer. It looks almost invisible and can make a single-pane window feel much closer to double-pane. It’s removable in spring.

Don’t Forget the Locks

Window locks pull the sashes tightly together when engaged. If your window is drafty even with weatherstripping, make sure it’s actually locked shut — not just closed. An unlocked window can let in a surprising amount of air through what looks like a closed seam.

A Few Hours, Real Savings

Most people can seal the drafty windows in their whole house in a single afternoon. The materials cost under $30 total for most homes. If you can feel a draft today, fix it before the first cold snap — you’ll notice the difference in both comfort and your next utility bill.

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