How to Fix a Drafty Window in 4 Steps

A drafty window isn’t just uncomfortable—it’s costing you real money every month. The Department of Energy estimates that weatherproofing windows can cut heating and cooling costs by 10–15%, and most drafty windows can be fixed in under an hour with about $30 in materials. You’ll know immediately if it worked because the cold spot or whistle will be gone.

This guide walks you through finding the leak, deciding which fix matches the problem, and doing the work yourself. Most drafts come from worn weatherstripping or cracked caulk around the frame—both straightforward weekend fixes. I’ll also flag the situations where the problem is bigger than a DIY repair, so you don’t waste time sealing a window that actually needs professional attention.

What you’ll need

For diagnosis:

  • Lighter or incense stick (to trace air movement)
  • Flashlight
  • Sticky notes or painter’s tape (to mark leak locations)

For weatherstripping replacement:

  • Flathead screwdriver or plastic pry tool
  • Replacement weatherstripping (V-channel for double-hungs, compression foam for casements)
  • Rubbing alcohol and clean cloth
  • Scissors or utility knife
  • Optional: hair dryer (to soften old adhesive)

For caulking:

  • Paintable acrylic-latex caulk (DAP or similar)
  • Caulk gun
  • Putty knife or caulk smoothing tool
  • Rubbing alcohol and cloth
  • Painter’s tape (optional, for clean lines)
  • Drop cloth
  • Utility knife

Prerequisites:

  • Access to both sides of the window (interior and exterior inspection)
  • Dry weather if you’re caulking exterior seams (caulk won’t stick to wet surfaces)

Before you start

Weatherstripping and caulking are low-risk projects—no electrical, no plumbing, no permits in most jurisdictions. The main safety consideration is ladder work if you’re sealing second-story windows from the outside. Use a stabilizer bar, work with a spotter, and don’t lean past your hips. If you’re not comfortable on a ladder, seal what you can from inside and hire a handyman for exterior work.

If you’re renting, check your lease before caulking. Adhesive-backed weatherstripping is almost always tenant-friendly because it’s removable; caulk is semi-permanent and may require landlord approval.

Step 1: Find the leak

Hold a lighter or lit incense stick about 2 inches from the window perimeter—top, bottom, sides, and where the sash meets the frame. On a windy day, you’ll see the flame flicker or smoke move sideways exactly where air is entering. Mark those spots with a sticky note or painter’s tape.

Check the bottom of the frame for visible gaps, condensation trails, or (in winter) frost patterns. Run your hand slowly along the sash and frame—you’ll feel cold air movement at the leak point.

Red flag: If you see condensation between the panes on a double- or triple-pane window, the seal has failed. That’s outside DIY scope—you’ll need a pro to reglaze or replace the unit.

What you’re looking for:

  • Gaps along the sash edges = weatherstripping failure
  • Cracks where the frame meets the wall = caulk failure
  • Visible light between sash and frame (more than a sliver) = warped frame or sash damage, which means a pro evaluation

Step 2: Clean the area thoroughly

Incense smoke revealing air draft at window frame.
Photo by Ron Lach on Pexels

This step makes or breaks the repair. New weatherstripping and caulk won’t stick to dust, loose paint, or old sealant residue.

Scrape away peeling caulk or weatherstripping with a flathead screwdriver or plastic pry tool. Vacuum out debris and dust. Wipe the frame and sash with a cloth dampened in rubbing alcohol—it evaporates fast and leaves no residue. Let it dry for at least 15 minutes before moving to the next step.

If you’re removing old adhesive-backed weatherstripping, warm it with a hair dryer on low heat for 30 seconds. The adhesive will soften and peel away cleanly.

Step 3: Apply weatherstripping or caulk (or both)

If the draft is along the sash edges—replace weatherstripping

Measure the perimeter of the movable sash (top, bottom, left, right). Buy replacement weatherstripping that matches your window type: V-channel (vinyl, accordion-fold) works for most double-hung windows; compression foam is better for casement windows or frames with uneven gaps; fin-style rubber is the most durable option for older wood frames.

Cut pieces to length with scissors or a utility knife. Apply adhesive-backed weatherstripping following the product directions—press firmly for 10–15 seconds per section to ensure contact. If your weatherstripping isn’t self-adhesive, tack it down with small finishing nails (1-inch, spaced every 4–6 inches).

Test it: Open and close the window a few times. It should move smoothly but feel snug when closed. If it sticks or binds, you’ve overlapped too much—trim the excess with a utility knife.

I’ve replaced weatherstripping on eight windows in the last two years, and every time I think I’ve bought too much, it turns out I need every inch. Measure twice.

If the draft is where the frame meets the wall—caulk the perimeter

If the gap is wider than half an inch, insert backer rod first. Press it into the gap with a putty knife so it sits about a quarter-inch below the surface. This prevents the caulk from sinking and cracking as it dries.

Load your caulk gun and cut the tip at a 45-degree angle, roughly matching the width of the gap. Apply painter’s tape along both sides of the seam if you want a clean line (remove it while the caulk is still wet).

Apply steady, even pressure as you pull the gun along the gap. The bead should fill the gap without overflowing. Immediately smooth it with a wet finger, putty knife, or caulk tool. One continuous stroke works better than lifting and re-pressing—you’ll see the difference in the finish.

Drying time: Acrylic-latex caulk is dry to the touch in about an hour and paintable within 3–4 hours. Check the product label. Don’t paint too early or the caulk will skin over and trap moisture underneath.

Don’t caulk the moving parts. Caulk seals the frame-to-wall joint, not the sash-to-frame gap where the window opens and closes. Sealing the moving parts will lock your window shut or make it bind.

Step 4: Test and verify

Deteriorated weatherstripping and cracked caulk on window.
Photo by Phil Evenden on Pexels

Once the caulk has set or the weatherstripping is in place, repeat the incense test. Air should no longer move through the sealed areas. Open and close the window several times—it should operate smoothly without sticking.

Check weatherstripping visually every six months during heating season. Compressed or cracked strips lose their seal and should be replaced. Caulk lasts longer (5–10 years depending on the product), but inspect it annually for cracks or gaps, especially on exterior seams that get sun exposure.

Troubleshooting

Problem: Weatherstripping sticks or makes the window hard to close

You’ve applied too much or overlapped pieces. Trim the excess with a utility knife or peel up one section and reapply it with less overlap.

Problem: Caulk cracked or pulled away within a year

The gap was too wide for the caulk alone, or the surface wasn’t clean. Re-clean the area, use backer rod for gaps over half an inch, and reapply fresh caulk.

Problem: I sealed everything but still feel a draft

Check the exterior. If the gap is between the frame and siding, interior caulk won’t help—caulk from the outside, or the leak may be coming from another window or door. Re-run the incense test on neighboring openings.

Problem: Window won’t stay open after I replaced weatherstripping

The sash cords or spring balance may be broken. That’s a separate repair—you’ll need to remove the sash to replace cords or hardware. It’s doable for confident DIYers but beyond the scope of a weatherstripping fix.

When to call a professional

Call a pro if you see:

  • Wood rot around the frame—soft, spongy wood or visible decay. Rot spreads and compromises the insulating value and structure. A pro will assess whether the frame can be repaired or needs replacement.
  • Condensation between the panes—the seal between double- or triple-pane glass has failed. Reglazed units are specialist work; replacement is often more cost-effective.
  • Visible light between the sash and frame (more than an eighth of an inch)—the sash is warped or the frame is out of square. Shimming or sash replacement may be needed.
  • Moisture damage or mold around the frame—suggests a water-infiltration issue (failed flashing, foundation grading problems). A pro should evaluate the cause before you seal anything, or you’ll trap moisture inside the wall.
  • Broken sash cords, springs, or locks—windows won’t stay open or close properly. Sash cord replacement requires removing the sash; spring or hardware failure usually means pro service.

Rough cost comparison:

  • DIY weatherstripping + caulk: $30–75
  • Professional weatherstripping service: $150–300
  • Professional sash-cord replacement: $200–400 per window
  • Window reglazing: $400–800 per window
  • Full window replacement: $500–1,500+ installed

I’ve hired pros twice—once for a sash-cord replacement on a 100-year-old double-hung (the cords were original and I didn’t want to crack the frame), and once for exterior caulking on a second-story window where I didn’t trust my ladder setup. Both times it was the right call.

FAQ

What causes drafty windows?

Drafty windows are usually caused by worn weatherstripping, cracked caulk, or gaps between the frame and wall. Over time, weatherstripping compresses and loses its seal, and caulk dries out and cracks from temperature swings. Older windows are more prone to drafts, but even new windows can leak if they weren’t installed correctly or if the sealant has failed.

Can you fix drafty windows yourself?

Yes, most drafty windows can be fixed with weatherstripping replacement or caulking—both straightforward DIY projects that take 30 minutes to 2 hours. You’ll need basic tools (caulk gun, screwdriver, utility knife) and $30–50 in materials. The exception is structural damage like wood rot, warped frames, or failed seals between panes, which require professional evaluation.

How much does it cost to fix a drafty window?

DIY fixes cost $10–50 in materials: weatherstripping runs $8–30 per roll, and caulk costs $5–15 per tube. Professional weatherstripping service costs $150–300. If the problem is a failed seal or rot, expect $400–800 for reglazing or $500–1,500+ for window replacement.

How long do weatherstripping and caulk last?

Foam weatherstripping lasts 2–5 years depending on wear; EPDM rubber weatherstripping can last 5–8 years. Acrylic-latex caulk lasts 5–7 years; polyurethane and silicone caulk last 10+ years. Inspect weatherstripping every six months during heating season and replace it when it looks compressed or cracked.

What’s the best sealant for windows?

For most interior window frames, paintable acrylic-latex caulk (like DAP) is the best choice—it’s affordable, easy to apply and clean up, and paintable within a few hours. For exterior seams or high-moisture areas, polyurethane (Sikaflex) or silicone caulk is more durable and flexible. Avoid non-paintable silicone unless you’re okay with the permanent finish.

Once you’ve sealed your drafty windows, the next step is maximizing their efficiency year-round. Pairing weatherstripping with the right window treatments can cut heat loss even further— window treatments for energy efficiency covers thermal curtains and cellular shades that work with your new seals. And if you’re tackling multiple weatherproofing projects, weatherproofing exterior doors uses the same techniques and materials.

Fixing drafts is one of the highest-return DIY projects you can do—lower heating bills, better comfort, and you’ll notice the difference the first cold night. For more on the energy-cost angle, save money on heating bills has a breakdown of how much weatherization actually saves per year.

We may earn a commission if you click links and make a purchase. See our affiliate disclosure for details.