Where the draft is coming from and how to find it
A drafty window usually leaks air at one of three places: the gap between the frame and the wall, the seal around the glass panes themselves, or the moving parts where the sash slides. The fastest way to find where yours is leaking is to light a stick of incense or hold a thin piece of tissue near the window on a windy day—the smoke or tissue will move toward the leak.
If the draft comes from the frame edges (where the window meets the wall), you are dealing with a perimeter seal problem. If it comes from the muntins (the strips between panes) or from around the glass itself, the glazing compound or caulk has failed. If it comes from the sash tracks or where the two sashes meet, the weatherstripping has worn out or the sash is warped.
Each location has a different fix, and knowing which one you have saves you from sealing the wrong spot. Spend five minutes finding the leak before you buy materials.
Key Takeaways
- Drafts come from three places—the frame-to-wall gap, the glazing around the glass, or the weatherstripping on moving parts—and you should locate yours before sealing.
- Caulk works for stationary gaps; weatherstripping works for moving parts; both are under $10 and take an hour or less per window.
- Remove old caulk completely before explore new caulk, or the new seal will fail within months.
- If the sash is warped or the glazing compound is crumbling, sealing alone will not hold—you may need to replace the sash or call a window professional.
Sealing the frame-to-wall gap with caulk
If the draft is coming from where the window frame meets the wall, caulk is the standard fix. Buy paintable acrylic latex caulk (around $3 to $5 per tube) and a caulk gun if you do not have one. Avoid silicone caulk for this job—it does not accept paint and is harder to remove later if you need to.
First, scrape out any old caulk, paint chips, or debris with a putty knife or caulk removal tool. This step is critical: new caulk will not stick to old caulk, and the seal will fail within a few months if you skip it. Use a damp cloth to wipe the gap clean and let it dry completely.
Load the caulk gun, cut the tube tip at a 45-degree angle (start with a small cut—you can always make it bigger), and run a steady bead along the gap. Smooth it with a wet finger or a caulk tool so it fills the gap completely and sits flush with both surfaces. Let it cure for the time listed on the tube (usually 24 hours) before painting.
Replacing weatherstripping on moving sashes
If the draft is coming from the sash tracks or where the two sashes meet, the weatherstripping has likely compressed or peeled away. Weatherstripping comes in several types: adhesive-backed foam, rubber gaskets, and spring-metal strips. Adhesive-backed foam is the easiest for a homeowner and costs $5 to $15 per window.
Remove the old weatherstripping by peeling it away slowly—if it resists, use a heat gun or hair dryer to soften the adhesive. Clean the track or sash edge with a dry cloth to remove all adhesive residue and dust. Measure the length you need and cut the new weatherstripping to fit, then peel the backing and press it firmly into place, working from one end to the other to avoid bubbles.
Test the sash movement after installation—it should slide smoothly without binding. If it feels tight, you may have applied the strip too thick or in the wrong spot. Peel it off and reposition it slightly inward.
Fixing failed glazing compound around the glass
If the draft is coming from the muntins or the edge of the glass pane itself, the glazing compound (the putty-like material that holds the glass in the frame) has cracked or shrunk. This is a more involved repair than caulking, but still manageable for a single pane.
Use a glazing tool or old putty knife to scrape out the old compound carefully—work slowly so you do not crack the glass. Once the glass is bare, clean the rabbet (the groove the glass sits in) with a dry cloth. Roll new glazing compound between your hands into a rope about the thickness of a pencil, press it into the rabbet all the way around the pane, and smooth it with a wet glazing tool or putty knife held at a 45-degree angle.
Let the compound cure for two to three weeks (check the package), then paint over it with exterior paint. If you have multiple panes or the glass itself is cracked, call a window professional—replacing the glass or the sash is beyond a typical homeowner repair.
When to use rope caulk as a temporary seal
Rope caulk is a sticky, putty-like cord that you press into gaps without a caulk gun. It is not permanent, but it works well as a temporary seal and costs $3 to $8 per roll. It is useful if you rent, if you want to avoid curing time, or if you want to test a seal before committing to permanent caulk.
Clean the gap with a dry cloth, then unroll the rope caulk and press it firmly into the gap with your finger, working around the entire frame. It will stay in place for one to two seasons before it hardens and loses grip. When you are ready to remove it, peel it away—there is no adhesive residue to clean up.
Rope caulk works best on small gaps (less than 1/4 inch wide). For larger gaps, permanent caulk is more reliable.
Sealing the sash when it is warped or does not close evenly
If the sash is warped or does not close evenly against the frame, weatherstripping and caulk alone will not stop the draft. A warped sash means the wood has absorbed moisture and swollen unevenly, and no seal can close a gap that changes size as the sash moves.
You have two options: sand and plane the sash to fit the frame again (a skilled carpentry job), or replace the sash entirely. If the window is old and the sash is original, a window professional can sometimes repair it. If the window is newer and the sash is warped under warranty, contact the manufacturer—they may replace it at no cost.
In the meantime, rope caulk or weatherstripping will reduce the draft, though it will not eliminate it completely.
Tools and materials you will need
| Job | Materials | Tools | Cost |
|---|---|---|---|
| Frame-to-wall gap | Paintable acrylic latex caulk | Caulk gun, putty knife, wet cloth | $5–$10 |
| Sash tracks or edges | Adhesive-backed foam weatherstripping | Heat gun or hair dryer, measuring tape, scissors | $5–$15 |
| Around glass panes | Glazing compound, exterior paint | Glazing tool or putty knife, brush | $10–$20 |
| Temporary seal | Rope caulk | None | $3–$8 |
Frequently Asked Questions
Can I caulk a window that is still wet or has condensation inside?
No. Caulk will not stick to wet surfaces and will fail within weeks. If you see condensation, open the window or run a dehumidifier for a few hours to dry it completely. If condensation keeps returning, you may have a moisture problem in the room—address that before sealing, or the moisture will build up behind the caulk.
What is the difference between paintable and silicone caulk?
Paintable acrylic latex caulk accepts paint and is easier to remove if you need to reseal later. Silicone caulk lasts longer but does not paint well and is messy to remove. For windows, paintable caulk is the better choice unless you specifically want a colored, unpainted seal.
How long does caulk last before it needs to be replaced?
Paintable acrylic latex caulk typically lasts five to ten years depending on sun exposure and weather. Silicone lasts longer—up to twenty years. If you see cracks, shrinkage, or gaps forming, it is time to reseal. You do not have to wait for failure.
Will sealing a drafty window reduce my heating bill?
Yes, but the savings depend on how many windows you seal and how drafty they were. A single sealed window might save $5 to $15 per heating season. If you seal all the drafty windows in your home, the total savings can be meaningful, but sealing is not a substitute for insulation or weatherstripping the whole house.
What should I do if the gap is wider than 1/2 inch?
Caulk and weatherstripping work best on gaps under 1/2 inch. For larger gaps, use backer rod (a foam rope you insert first) before caulking, or call a window professional to check whether the frame has shifted or settled. A gap that wide sometimes signals a structural issue.