How to Seal Windows for Winter

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Depending on the age and condition of your house, you could be losing up to 30% of your heat through your windows. Some of this heat loss is through the glass itself in the form of convection or radiation. Shades or other tight-fitting window coverings will reduce this heat loss. But a lot of heat is also lost through cracks around the window or through gaps in the weatherstripping. Sealing the cracks and repairing or adding to the weatherstripping is the best way to stop these leaks. And it’s usually the most cost-efficient way to save energy. A tube of caulk used to seal gaps around a window will pay for itself several times over in energy savings. But how do you know where to start? Here are some tips for how to seal windows for winter:

Caulk around the interior trim

On a cold, windy day, feel around your windows to try to determine where the air is leaking in. Check along the outside edge of the window molding. You can also use a stick of burning incense and watch the smoke as you move it around your window. Seal leaks around the trim with caulk. If your trim is painted, use caulk that matches the color of the trim. Acrylic latex caulk is fine for this job. This guide will help you choose the right caulk for the job..

An extra buck or two for good quality caulk is money well spent. If your trim is unpainted wood, look for caulk that dries clear or that matches the wall color. And one last thing, when you prepare the caulk tube by cutting off the tip, be careful to remove just enough to create a very small opening—about the size of a single piece of spaghetti. This will allow you to create a narrow, neat bead without a lot of extra caulk to clean up.

Here are some additional tips for getting a neat caulk job.

Repair or augment weatherstripping

After checking around the window moldings for leaks, move to the window itself. Anywhere the movable part of the window contacts the window frame is a potential air leak. Of course, when the window was new, these areas were sealed with weatherstripping. But worn out weatherstripping, and shifting window frames, can open up gaps over time. Here’s where some detective work is in order. If you’re lucky enough to know or find the brand of your window, you may be able to contact the manufacturer for replacement parts. In some cases the weatherstripping simply fits in a groove and can be slid out and replaced if it’s damaged. But if you can’t find replacement weatherstripping, or large gaps have opened that can’t be sealed by the original weatherstrip, then you’ll have to look for an add-on type seal that will work. Hardware stores and home centers have a large selection and you’re bound to find one that will do the trick.

Here’s how to repair old casement windows.

Seal the exterior with caulk

Filling any gaps around the exterior perimeter of your windows with caulk will help prevent air leakage, and has the added benefit of keeping water out of your walls. This technique won’t work with vinyl siding though, since the vinyl expands and contracts too much and is usually contained in a channel that makes it impossible to caulk anyway. But for most other types of siding, it pays to seal the space between the exterior trim and siding with caulk. If you’re skilled with a caulk gun and don’t mind having to use a volatile solvent like mineral spirits to clean up, urethane-based caulks offer one of the longest lasting solutions, but any good-quality exterior caulk will do a fine job. Check out this collection of tips and tricks to make exterior caulk last longer.