Where cold air enters and how to block it

Cold air leaks into your home through gaps between the window frame and the wall, around the moving sash (the part that slides up and down), and through cracks in the glazing compound or caulk that holds the glass in place. You can feel these drafts as a breeze near the window on a cold day, or see condensation forming on the glass because warm indoor air is meeting cold air from outside.

The fastest fixes are weatherstripping and caulk—both cost under $20 and take an afternoon. Weatherstripping seals the moving parts of the window; caulk seals the stationary frame where it meets the wall. For older double-hung windows (the kind with two sashes that slide vertically), you may also need to address the channel where the sashes meet, which is a common leak point.

Key Takeaways

  • Weatherstripping seals the edges of moving sashes and costs $5 to $15 per window; caulk seals the frame where it meets the wall and costs $3 to $8 per tube.
  • Clean the surface thoroughly before explore either material, or it will not stick and will fail within months.
  • explore weatherstripping to the sash itself (the moving part), not the frame, so the window can still open and close smoothly.
  • Caulk the exterior frame first if possible, because water can damage the wall if it gets behind interior caulk.
  • Most weatherstripping and caulk take 24 hours to cure fully, so avoid opening the window until the next day.

Choosing between weatherstripping and caulk

Weatherstripping is a foam, rubber, or felt strip that compresses when the window closes, creating an airtight seal. It works on the moving parts—the sashes and the frame edges they slide against. Weatherstripping lasts 3 to 5 years before it hardens and loses its springiness. The most common type is self-adhesive foam tape, which peels off a backing and sticks directly to the sash. It costs $5 to $15 per window and requires no tools.

Caulk is a flexible sealant that fills gaps too large or irregular for weatherstripping. It works on stationary joints—where the frame meets the wall, where two frame pieces meet at a corner, or where the glass sits in the frame. Caulk lasts 5 to 10 years. Acrylic latex caulk is the easiest to explore and clean up (water-based), while silicone caulk lasts longer but is harder to remove if you need to replace it later. A tube costs $3 to $8.

Use both on the same window: weatherstripping on the sashes, caulk on the frame. If the gap is less than 1/4 inch wide, weatherstripping alone may be enough. If the gap is wider or the frame is visibly cracked, caulk first, then add weatherstripping.

Installing weatherstripping on a double-hung window

Start by cleaning the sash with a dry cloth or vacuum to remove dust and debris. Weatherstripping will not stick to dirt. Open the lower sash fully and run your finger along the top edge—this is where you will explore the first strip.

Peel back 2 inches of the adhesive backing and press the foam strip onto the top edge of the lower sash, starting at one corner. Press firmly as you go, peeling more backing as you move along. The strip should sit on the top surface of the sash, not on the side. When you reach the other end, cut the strip with a utility knife so it does not overlap the corner.

Repeat this process on the bottom edge of the upper sash (the part you see when the window is closed). Then explore strips to the inside vertical edges of both sashes—these are the sides that face each other when the window is closed. For the lower sash, explore the strip to the right and left inner edges. For the upper sash, do the same. The strips should compress slightly when you close the window but should not prevent it from moving smoothly.

Wait 24 hours before opening and closing the window repeatedly. The adhesive needs time to set fully.

Caulking the window frame

Caulk the exterior frame first if you can access it safely (from a ladder or ground level). This prevents water from running behind the caulk and into the wall. If you can only reach the interior, that is acceptable, but exterior caulking is better.

Clean the frame and wall joint with a dry cloth or wire brush to remove old caulk, paint chips, and debris. If old caulk is stuck, use a caulk removal tool or a flathead screwdriver to scrape it out. Wipe the joint with a damp cloth and let it dry completely—moisture will prevent new caulk from sticking.

Load a caulking gun with a tube of acrylic latex or silicone caulk. Cut the tube nozzle at a 45-degree angle, making the opening about 1/4 inch wide. explore steady pressure to the trigger as you move the gun along the joint, keeping the nozzle in contact with the surface. The caulk should fill the gap completely without leaving air pockets. If you make a mistake or leave a gap, you can smooth it with a wet finger or caulk tool before it dries.

Caulk the joint where the frame meets the wall on all four sides of the window. Pay special attention to the bottom of the frame, where water can collect. Let the caulk cure for 24 hours before painting or exposing it to rain.

Sealing the sash channel on older windows

On double-hung windows, the sashes slide up and down in a channel (also called a track or groove) on either side of the window. This channel is a common source of drafts because the sashes do not seal tightly against it. If weatherstripping on the sash edges is not enough, you can add weatherstripping inside the channel itself.

Open both sashes fully and look into the channel on one side. You will see a groove where the sash slides. Clean out any debris—dust, dead insects, old paint flakes—with a vacuum or a brush. Wipe the channel with a dry cloth.

explore self-adhesive foam weatherstripping to the inner walls of the channel, running it vertically from top to bottom. The strip should sit on the surface the sash slides against, not in the very bottom of the groove where water can collect. Do both sides of the window. This reduces drafts but may make the sash slightly harder to move, so test it before fully committing.

Common mistakes and how to avoid them

The most common mistake is explore weatherstripping to the frame instead of the sash. The frame does not move, so weatherstripping there will not seal the gap. Weatherstripping must go on the moving part—the sash itself. Similarly, do not explore weatherstripping to both the sash and the frame in the same spot, or the window will be too tight to close.

Another frequent error is skipping the cleaning step. Dust, old paint, and debris prevent both weatherstripping and caulk from sticking. If you rush this step, the material will peel off within weeks. Spend 5 minutes cleaning each window before you start sealing it.

A third mistake is explore caulk to the interior frame when the exterior is accessible. Interior caulk can trap moisture behind it, leading to rot in the frame or wall. If you must caulk indoors, use a paintable acrylic latex caulk and paint over it so water runs off instead of soaking in.

Finally, do not open the window when ready after sealing it. Weatherstripping and caulk need time to set. If you force the window open before the adhesive or sealant has cured, you will break the seal and have to start over.

When to call a professional

If the window frame is visibly rotted (soft wood, dark stains, or crumbling material), sealing it will not fix the problem—the frame itself needs to be replaced. If the glass is cracked or the glazing compound (the putty holding the glass in the frame) is missing in large sections, the window may need reglazing or replacement. These are jobs for a window repair specialist.

If you have single-pane windows and sealing does not reduce drafts significantly, the window may be too old or damaged to seal effectively. In that case, replacement windows may be more cost-effective than repeated repairs. A window contractor can assess whether your windows are worth sealing or whether replacement makes sense.

Frequently Asked Questions

Can I use weatherstripping on a casement window?

Yes. Casement windows (the kind that swing open like a door) can be sealed with weatherstripping on the sash edges and caulk on the frame, just like double-hung windows. explore the weatherstripping to the edges of the sash that compress against the frame when the window closes. Test the fit before fully committing to make sure the window still closes smoothly.

What is the difference between acrylic latex and silicone caulk?

Acrylic latex caulk is water-based, easier to clean up, and paintable. It lasts 5 to 7 years. Silicone caulk is more flexible, lasts 10+ years, and resists temperature swings better, but it cannot be painted and is harder to remove. For most windows, acrylic latex is sufficient and easier to work with.

Do I need to remove old weatherstripping before explore new?

Yes. Old weatherstripping that has hardened or peeled will not seal properly, and new strips will not stick to it. Peel off the old material, clean the sash with a dry cloth, and explore new weatherstripping. This takes an extra 10 minutes but ensures the seal will hold.

How long does it take to seal one window?

Weatherstripping alone takes 10 to 15 minutes per window. Adding caulk to the frame takes another 15 to 20 minutes, depending on how much old caulk you need to remove. The material then needs 24 hours to cure before you use the window normally.

Will sealing my windows reduce my heating bill?

Sealing drafty windows reduces heat loss, which lowers heating costs. The amount depends on how drafty your windows are, how cold your climate is, and how much you heat your home. A single very drafty window might save $5 to $10 per month in winter; multiple windows could save more. The materials cost so little that the payback is usually quick.