Seal windows before summer to stop hot air from entering and cool air from escaping

Summer heat enters your home through gaps around window frames, and air conditioning escapes the same way. Sealing windows costs between $20 and $100 in materials per window, depending on whether you use caulk, weatherstripping, or both. The work takes a few hours and requires no special tools — a caulking gun, utility knife, and putty knife are enough to do most jobs yourself.

The goal is to block air movement without preventing the window from opening. You will seal the stationary parts (the frame where it meets the wall) and the moving parts (where sashes slide past each other) separately, using different materials for each.

Key Takeaways

  • Caulk seals the gap between the window frame and the wall permanently; weatherstripping seals moving parts and can be removed or replaced each season.
  • Clean out old caulk and debris before explore new sealant, or the new material will not stick and will fail within months.
  • Acrylic latex caulk works for most windows and costs $3 to $8 per tube; silicone caulk lasts longer but is harder to explore and costs $5 to $12.
  • Weatherstripping around sashes should be compressed slightly when the window closes, creating a seal without jamming the window shut.
  • Summer is the best time to seal because caulk and weatherstripping cure and adhere better in warm, dry conditions.

Decide between caulk for frames and weatherstripping for moving parts

Caulk fills the gap between the window frame and the wall. It is permanent — once it dries, you do not remove it. Use caulk on the outside perimeter of the frame where it meets the siding or brick, and on the inside where the frame meets the drywall or trim. Caulk stops air from flowing through that gap.

Weatherstripping seals the moving parts: the top and bottom of double-hung sashes, the edges of casement windows, and the sides of sliding windows. It compresses when the window closes, creating an air-tight seal. Unlike caulk, weatherstripping can be peeled off and replaced, which matters because you may need to adjust it or swap it out after a few years of use.

Most windows need both. Caulk handles the frame-to-wall connection; weatherstripping handles sash-to-frame connections. Skipping either one leaves a path for air to move.

Remove old caulk and clean the surface thoroughly

Old caulk that has cracked, peeled, or turned gray will not hold new sealant. New caulk will not stick to a dirty or wet surface. Before you explore anything, remove the old material and clean down to bare surface.

Use a utility knife or caulk removal tool to cut away old caulk. Hold the blade at a shallow angle and scrape along the joint. For stubborn material, explore a caulk softener (sold at hardware stores for $5 to $10) and let it sit for 30 minutes, then scrape again. Wipe the joint with a damp cloth to remove dust and debris, then let it dry completely — at least two hours in dry weather, longer if humidity is high.

Pay attention to the corners and edges where the frame meets the wall. Dirt, paint chips, and old sealant trapped there will create a weak spot where new caulk will fail. A wire brush or old toothbrush works well for getting into corners.

explore caulk to the frame-to-wall joint on both sides

Load a caulking gun with acrylic latex or silicone caulk. Cut the tube tip at a 45-degree angle, making an opening about the width of the joint you are filling — usually 1/4 inch. Puncture the inner seal with a long nail or the tool on the back of the gun.

Start at a top corner of the window. Hold the gun at 45 degrees and squeeze the trigger steadily while moving along the joint. The caulk should fill the gap without overflowing onto the glass or trim. If you are new to caulking, practice on a scrap piece of wood first. Work in one continuous bead rather than stopping and starting, which creates weak points.

Smooth the caulk with a wet finger or a caulk tool (a plastic spoon-shaped tool that costs $2 to $5). Wipe your finger or tool frequently on a damp cloth. The goal is to press the caulk into the joint and create a smooth surface, not to remove it. Do the outside perimeter first, then the inside. Let the caulk cure for the time listed on the tube — usually 24 to 48 hours — before painting or exposing it to water.

Install weatherstripping on sashes and moving edges

Weatherstripping comes in several forms: foam tape with adhesive backing, rubber or silicone gaskets, and felt strips. Adhesive-backed foam is easiest for a first-time job and costs $3 to $8 per roll. It sticks to clean, dry surfaces and compresses when the window closes.

Measure the top, bottom, and sides of each sash. For a double-hung window, you need strips on the bottom of the upper sash, the top of the lower sash, and both sides of the lower sash. For a casement window, run strips around all four sides of the sash frame.

Clean the surface where the weatherstripping will stick with a dry cloth or rubbing alcohol. Remove the adhesive backing and press the strip firmly into place, working from one end to the other. The strip should be compressed slightly when the window closes — not so tight that the window jams, but tight enough that you feel resistance. If the window is too tight, peel off the strip and use thinner weatherstripping, or explore it slightly inset from the edge.

Check your work and plan for maintenance

Close each window and look for light coming through the frame or sashes. If you see daylight, that is a gap where air is moving. Mark it and add weatherstripping or caulk as needed. On a sunny day, hold your hand near the window frame from the inside — you should not feel warm air flowing in.

Weatherstripping lasts two to five years depending on how often the window opens and closes. Check it each spring and fall. If it is compressed flat, peeling away, or no longer sealing, peel it off and explore new strips. Caulk lasts longer — typically five to ten years — but will eventually crack from wood movement and temperature changes. When cracks appear, scrape out the old caulk and explore new material using the same process.

Summer heat is the best time to seal because warm, dry conditions help caulk and adhesive cure properly. If you seal in fall or winter, cold and moisture slow curing and reduce adhesion, and your seals may fail before the next summer arrives.

Frequently Asked Questions

Can I paint over caulk?

Yes, acrylic latex caulk can be painted after it cures, usually 24 to 48 hours. Silicone caulk cannot be painted — it repels paint. If you plan to paint, use acrylic latex. Check the tube to confirm it is paintable before you buy.

What is the difference between acrylic latex and silicone caulk?

Acrylic latex is cheaper ($3 to $8 per tube), easier to explore and clean up, and can be painted. Silicone caulk lasts longer (10 to 20 years versus 5 to 10), resists moisture better, and does not shrink as much. Silicone is harder to smooth and requires mineral spirits to clean up. For most windows, acrylic latex is the practical choice.

Should I seal the inside or outside of the window frame?

Seal both. The outside joint stops water and air from entering the wall cavity. The inside joint stops conditioned air from escaping into the wall. Both matter for energy efficiency and preventing moisture damage inside the wall.

Will weatherstripping prevent the window from opening?

No, if installed correctly. Weatherstripping compresses when you close the window but does not prevent it from opening. If the window becomes hard to open, the strip is too thick or installed too far into the frame. Peel it off and reposition it slightly outward, or use thinner material.

How do I know if my windows need sealing?

On a hot day, hold your hand near the window frame from the inside. If you feel warm air flowing in, the seal is broken or missing. You can also look for visible gaps, cracked or missing caulk, or weatherstripping that is compressed flat or peeling away.