How To Seal Windows and Doors for Winter

As winter approaches, homeowners often find themselves battling drafts and rising energy bills. Thankfully, properly sealing your windows and doors can help. In the video above, This Old House general contractor Tom Silva reveals his most effective techniques for sealing windows and doors to keep the cold air out and the warm air in.

Common Areas of Heat Loss

Windows and doors are the primary culprits of heat loss in homes. Here are some common areas where heat escapes:

• Cracks in the window pane or frame
• Gaps between the door and the frame
• Gaps between the window frame and the wall
• Spaces between the door and the floor
• Spaces between the sash and frame
• Worn or damaged weather stripping

Pro Tip: Don’t underestimate door gaps. As TOH host Tommy Silva points out, an eighth-inch crack around the front door and back door lets as much air into the house as if you had a small window open halfway. “There are all kinds of door sweeps that you can install on the bottom of the door,” he says, from surface-mounted types to ones that sweep up the sides and across the top.

Techniques for Sealing Windows

There are several ways to seal windows effectively for winter. The best approach depends on the type of window and the specific issues you’re facing, but here are common techniques:

• Foam tape: Foam tape is particularly useful for sealing irregularly shaped gaps. Carefully measure and cut the tape to size to cover the entire gap.
• Temporary caulking: For windows that you won’t open until spring, seal them shut with temporary caulking. You can press it into place and easily peel it off when winter is over. This method is quick, easy, and reversible.
• Weatherstripping: Weatherstripping is an effective way to seal gaps around movable window parts. Measure the length of each side of the window and cut the weatherstripping to fit. Make sure to test the window to ensure it still opens and closes smoothly.

Shrink-Wrap Plastic Film: For windows you won’t need to open all winter, consider covering the inside of the window opening with special plastic film that comes in a kit and is held in place with double-sided tape. A hair dryer shrinks the clear plastic to form a wrinkle-free, see-through seal. According to TOH Magazine, this inexpensive clear shrink film can allow a room to retain as much as 55 percent of its heat. In a pinch, bubble wrap makes an effective replacement — just push the bubble side against the glass and adhere with double-sided tape.

Sealing Double-Hung Windows

Double-hung windows require special attention because of their design. Silva emphasizes the importance of using sash locks on these windows to close the gap along the meeting rail. Here’s how he does it:

1. Close the window completely.
2. Engage the sash locks to pull the upper and lower sashes together.
3. For wide windows, consider installing two sash locks for a tighter seal.
4. To prevent air leakage at the top of the window, apply adhesive-backed foam weather stripping to the top edge of the upper sash. The foam should compress slightly when the window is closed.
5. Use foam or rubber backer rod to fill large gaps between the lower sash and the sill. Cut the backer rod to size and force it into the space.

Pro Tip: Norm Abram, TOH master carpenter, explains why sash locks matter for more than security: “A good sash lock on a double-hung window discourages break-ins and keeps out drafts by pulling the top and bottom sashes tightly together and pushing each one snug against the top and bottom of the window opening.”

Techniques for Sealing Doors

It’s equally important to seal doors to prevent drafts. Here are some common methods:

• Foam tape for gaps: Foam tape can be useful for doors with uneven gaps. Clean the area thoroughly, measure and cut the tape to fit the gap, and press it firmly into place. 
• Installing a door sweep: Install a door sweep along the bottom of exterior doors. Choose a sweep made of durable materials that can withstand constant opening and closing. The sweep should make contact with the threshold without causing resistance.
• Weatherstripping: Apply weatherstripping to the sides and top of the door frame to create a tighter seal. This prevents air from leaking in around the door’s edges. You can also add weatherstripping around the doorjamb.

Expert Insight: Tom Silva puts the stakes in perspective: “Just like a refrigerator door needs a good seal to keep cold air in, exterior doors need a good seal to keep cold air out.” He notes that a door’s weather seals can rip, compress, bend, or wear out over time, leaving chilly winter air free to enter — but attaching new weather seals is a straightforward exercise, far cheaper and faster than installing a new door.

Don’t Forget Interior Doors: It’s not just the front and back doors that you need to worry about. Cold air can also enter the house through gaps around any door leading to an uninsulated space, such as a garage or basement. Weatherstrip the top and sides, and add a door sweep to the bottom. Also, one of the biggest sources of air infiltration around a door is between the jamb and the framing — filling that gap with expanding polyurethane foam seals off drafts better than fiberglass, but use it sparingly, as too much can bend the jamb.

Pro Tip: Tom Silva, This Old House general contractor, recommends a wood sweep that you can stain or paint to match your door and that has an attached nylon brush to follow the contours of irregular flooring or carpeting. His preferred method for sealing the bottom of an entry door involves routing a groove in the bottom edge to accept a silicone gasket that remains hidden from view, though he notes that an easier-to-install visible sweep that screws to the bottom face of the door works just as well.

Addressing Other Air Leaks

While windows and doors are the biggest culprits, they’re not the only potential sources of air leaks in your home.

Sealing Electrical Outlets

Surprisingly, electrical outlets on exterior walls can be a significant source of air infiltration. TOH  host Kevin O’Connor says that 2%–5% of air infiltration in a house comes from around outlets. Follow these steps to address this issue:

1. Remove the outlet cover plate.
2. Install a soft rubber gasket over the outlet.
3. Replace the cover plate.

This simple process can significantly reduce air leakage through these easily overlooked areas.

Pro Tip: When sealing outlets, remember that the goal is to seal the gap between the electrical box and the drywall — not to fill the entire wall cavity with foam. As one TOH expert explains: “You’re not asking me to seal the gap between the actual outlet in the box. You’re asking me to seal the box in the drywall… you’re trying to seal the air to let the air be the insulator. You don’t really want to fill that with foam inside that whole space.”

Filling Gaps Around Wall Penetrations

Holes drilled for cables, vents, and pipes can allow cold air to enter your home. Follow these steps to seal them:

1. Identify all wall penetrations.
2. Clean the area around each hole.
3. Use minimal expanding foam to fill the gaps.
4. Once dry, trim any excess foam.

Chimneys and Ducts

Chimneys, flues, and ducts can also allow cold air to seep into your home. Inspect these areas and seal any gaps with appropriate materials, such as high-temperature caulk or durable weather stripping. Keep the fireplace damper closed when you’re not using it to prevent drafts.

Pro Tip: A roaring fire can actually pull cold air into your house through cracks around windows and doors by creating a convection current. To minimize this effect, close the doors to the room where the fireplace is in use, and crack a nearby window slightly so the fire draws from that fresh air supply instead of pulling heated air from the rest of the house. When the fire is out, make sure the damper seals tightly—if it doesn’t close properly, warm air will continuously escape up the chimney.

Duct Sealing: For HVAC ducts and exhaust ducts, spread fiber-reinforced mastic on all joints rather than using cloth-backed “duct tape,” which tends to fall off within a year. For longitudinal seams, use foil tape; for elbows and irregular-shaped joints, brush on mastic plenty thick to fill every gap. Once all joints are sealed, wrap the supply ducts with R-5 or R-6 foil-faced fiberglass insulation—foil on the outside, fiberglass on the inside—to prevent further heat loss.

Sealing Windows and Doors: Sustainable Choices

For those concerned about their environmental impact, there are eco-friendly sealing options available. Look for products made from recycled materials or sustainable sources. Many weatherstripping and caulking products are designed to reduce your carbon footprint while enhancing your home’s efficiency.

Home Air Sealing: Cost Considerations

Consider the cost of each sealing option. Temporary solutions, such as foam tape, are generally less expensive. More permanent solutions like weatherstripping cost more but last longer. Here are some typical prices for different materials at big-box hardware stores:

• Backer rod: $0.50 per foot
• Foam tape: $0.50 per foot
• Temporary caulk: $10 per tube
• Weatherstripping: $2.50 per foot

Professional Assistance

Homeowners who are unsure about the best sealing materials or techniques can consult an energy auditor or weatherization specialist. These professionals can assess your home and recommend the most effective methods.

What You’ll Need