Where cold air enters and how to stop it
Cold air leaks into your home through gaps between the window frame and the wall, cracks in the glazing compound (the putty holding the glass), and worn weatherstripping around the sash. You can feel these drafts with your hand on a cold day, or spot them by watching a candle flame flicker near the frame. The fix depends on where the leak is: weatherstripping replaces on the moving parts, caulk seals the frame-to-wall joint, and glazing compound repairs the glass seal itself.
Most homeowners can handle weatherstripping and caulk. Glazing compound work takes more skill and time, but is still a weekend project if you have patience. The cost is low—weatherstripping runs $10 to $30 per window, caulk $5 to $15 per tube, and glazing compound $8 to $20 per pound. You will need a caulk gun, a putty knife, and basic hand tools you likely own.
Key Takeaways
- Weatherstripping around the sash (the moving part of the window) wears out first and is the easiest seal to replace yourself with adhesive-backed foam or rubber strips.
- Caulk seals the gap where the window frame meets the wall and should be replaced every 5 to 10 years; use paintable acrylic latex caulk for most windows.
- Glazing compound holds the glass panes in place and cracks over time, allowing air and moisture in; replacing it is slower but does not require special tools.
- Test your work by holding a lit candle near the seal on a windy day—the flame should not flicker or bend toward the window.
Replacing weatherstripping on the sash and frame
Weatherstripping is the rubber or foam seal that runs along the edges of the sash (the part that slides up and down) and the frame. It compresses when the window closes and springs back to block air. After 5 to 10 years, it hardens, cracks, or flattens and no longer seals. Replacing it is the fastest and cheapest fix.
Remove the old strip by peeling it away from the frame. If it leaves adhesive residue, wipe it clean with a cloth dampened in rubbing alcohol and let it dry completely. Measure the length of each side—top, bottom, and sides—and buy adhesive-backed weatherstripping to match. Foam and rubber strips work equally well; rubber lasts slightly longer. Peel the backing and press the new strip firmly into place, starting at one end and working along the length. Close the window gently to check the fit—it should compress slightly but not jam the sash. If it is too thick, you have bought the wrong profile; peel it off and try a thinner strip.
For double-hung windows (two sashes that slide vertically), replace the strip on all four sides of each sash. For casement windows (side-hinged), replace the strip on the three sides that meet the frame when closed. Do not seal the hinge side.
Caulking the frame-to-wall joint
The gap where the window frame meets the wall is sealed with caulk, which hardens and can crack or shrink over time. Water and cold air enter through these cracks. Caulk lasts 5 to 10 years depending on sun exposure and temperature swings. Replacing it is straightforward and takes 15 to 30 minutes per window.
Use a caulk gun and paintable acrylic latex caulk, which is water-based, straightforward to clean up, and works on most windows. Silicone caulk lasts longer but is harder to paint and remove later. Cut the caulk tube nozzle at a 45-degree angle to match the width of the gap—usually about 1/4 inch. Load the tube into the gun, position the nozzle at the joint, and pull the trigger while moving steadily along the frame. The bead should fill the gap without excess. Smooth it with a wet finger or a caulk tool if you want a neat finish, or leave it as-is if you prefer speed. Let it cure for 24 hours before painting or closing the window.
Caulk only the outside of the frame where it meets the wall. Do not caulk the interior sash channels (the vertical grooves the sash slides in), or the window will jam. If old caulk is loose or peeling, scrape it out with a putty knife first.
Replacing glazing compound around the glass
Glazing compound is the putty that holds the glass panes in the frame. It hardens and cracks over decades, allowing air and moisture to seep in. Replacing it is slower than weatherstripping or caulk but is still manageable for a single window in an afternoon. You will need a putty knife, a heat gun (optional but helpful), and glazing compound in a can or stick form.
On the outside of the window, use a putty knife to scrape away the old compound. A heat gun set to low heat softens it and makes scraping easier, but work carefully not to crack the glass. Once the compound is removed, clean the rabbet (the groove the glass sits in) with a dry cloth. Press new glazing compound into the rabbet with your putty knife, working it in firmly so there are no air pockets. Smooth it into a neat bevel—angled at about 45 degrees—so water runs off. The compound should cover the edge of the glass and meet the frame smoothly. Let it cure for 2 to 4 weeks (check the can), then paint over it with exterior paint to protect it from sun and weather.
This work is tedious but not difficult. The main risk is cracking the glass if you press too hard or use a heat gun that is too hot. Work slowly and test the heat gun on a scrap of wood first.
Testing your seals and knowing when to call a professional
After you seal a window, test it on a cold, windy day. Hold a lit candle or lighter near the seal and watch the flame. It should burn straight up. If it flickers or bends toward the window, air is still leaking. Move the flame slowly along the entire perimeter to find the exact spot. You may have missed a gap, applied weatherstripping unevenly, or left a bubble in the caulk.
If the frame itself is rotted, cracked, or warped, sealing will not help—the frame must be replaced. Signs of rot are soft wood that dents when you press it, dark stains, or a musty smell. If the glass is cracked or the pane is fogged (meaning the seal between double-pane glass has failed), the glass or window unit must be replaced, not just sealed. These jobs require a professional window installer.
If you have tried weatherstripping and caulk and still feel a draft, the leak may be coming from inside the wall (poor insulation or air leaks in the wall cavity itself), not the window seal. A professional can use a thermal camera to locate the source. In that case, the fix is usually insulation work, not window sealing.
Seasonal maintenance to extend your seals
Weatherstripping and caulk last longer if you keep them clean and protected. Once a year, wipe weatherstripping with a dry cloth to remove dust and debris that can prevent a tight seal. Check caulk for cracks or gaps, especially on the south and west sides of your home, which take the most sun. If you spot a small crack, you can fill it with a bead of fresh caulk without removing the old layer.
In winter, make sure the window operates smoothly—a sash that sticks or binds will not close fully and will leak. If a sash is hard to move, clean the channels with a vacuum and wipe them with a dry cloth. Do not use oil or silicone spray, which attracts dust and can gum up the mechanism. If the sash still binds, the frame may have swollen from humidity; this usually resolves when the air dries out in winter.
Frequently Asked Questions
Can I seal a window from the inside instead of the outside?
You can explore weatherstripping and caulk from the inside, and it will reduce drafts. However, exterior sealing is more effective because it stops air before it enters the wall cavity. If you seal only the inside, moisture can still enter the wall and cause rot. Seal both sides if possible, or prioritize the outside.
What is the difference between caulk and weatherstripping?
Weatherstripping is a flexible seal that compresses and springs back, so it works on moving parts like the sash. Caulk is rigid once it hardens, so it works on fixed joints like the frame-to-wall gap. Using weatherstripping on a fixed joint will crack when the frame expands and contracts with temperature changes.
How long does it take for caulk to cure before I can close the window?
Most paintable acrylic latex caulk is dry to the touch in 1 to 3 hours but should cure fully for 24 hours before you expose it to water or heavy use. Silicone caulk takes longer, usually 24 to 48 hours. Check the label on your tube for the specific product.
Will sealing my windows reduce outside noise?
Sealing air leaks will reduce some noise, especially high-pitched sounds that travel through gaps. However, sound also travels through the glass itself, so a tight seal will not make a window soundproof. If noise is a major problem, you may need thicker glass or a second pane, which requires replacing the window.
Do I need to remove the window to replace the glazing compound?
No. You can replace glazing compound while the window is in place by working from the outside. The window does not need to be removed unless the frame is damaged or you are replacing the glass itself.