This story shows you how to weather-strip windows.
Most heat loss at a window occurs through gaps between the sashes and the frame. Even small gaps can be big energy-wasters. On a windy day hold a piece of tissue paper or plastic wrap near the window and move it around. Wherever you see movement (either outward or inward), there is a significant leak.
The first step is to caulk, especially on the exterior, although some interior caulking is helpful as well. Also check that the glazing putty on the outside is free of gaps and seals tightly against the window. Where glazing is failing, scrape it out and apply new glazing. On the inside, see that the joint between the glass and the sash is sealed with paint.
Weather-stripping where two surfaces push together (the horizontals of a double-hung window and the verticals of a casement or sliding window) is straightforward. Where two surfaces slide against each other (the verticals of a double-hung window and the horizontals of a casement or slider) calls for more precision.
1 or 2 hours to apply weather-stripping to all the moving parts of a double-hung window
Tape measure, tin snips, scissors, caulk gun, hammer, drill
Measuring, cutting with tin snips, driving small nails
Determine where your window needs weather-stripping
Weather-stripping, brads, caulk, spray foam insulation, fiberglass insulation, rags, and perhaps mineral spirits
Nail-on weather-stripping is the most durable choice if you have a wood window. Spring bronze works well for gaps that are consistent in width. It is also the best-looking product. Where the gap is large and uneven and looks are not as important, a tubular vinyl gasket is a good choice. Strips of felt (not shown) are a poor choice because they don't seal well and are not durable.
Self-stick weather-stripping is easy to cut, making it the most convenient choice. If you are choosing self-stick V-strip tape, be sure it is made of EPDM (ethylene-propylene-diene-monomer), which stays flexible for many years, even when exposed to extremely low temperatures.
Foam weather-stripping is easy to apply and fills large and uneven gaps effectively. However, it usually doesn't last long. Open-cell foam is the best at bouncing back after being compressed, but it can only be used on the inside. Closed-cell foam is weather resistant but short-lived.
For quick but temporary sealing, use rope caulk, which can be removed when the weather gets warm.
A double-hung window has a number of potential leak points. Most prominent are where the bottom of the upper sash meets the top of the lower sash, where the sashes slide against the jamb, and where the bottom sash meets the stool. These gaps must be sealed with weather-stripping. Gaps can also be found on the outside of the casing, the underside of the stool, and the apron. To seal them, paint and caulk.
Cut a caulk tube's tip using a sharp utility knife; a straight, clean cut contributes to a smooth caulk line. Some people prefer to cut at a steep angle, while others prefer a nearly straight cut. Cut near the tip for a small bead of caulk. Some caulk tubes require the seal be broken with a wire or long nail through the tip.
It takes a bit of experience to produce a smooth bead of caulk, so start caulking in an inconspicuous location. Get in a comfortable position and rest the tip against the joint. Squeeze the trigger until caulk emerges, then continue to squeeze as you move the tip along the joint.
If you have installed a replacement window or replacement sashes, the cavity for the sash weights can be filled with insulation. Fill the opening by gently stuffing with fiberglass insulation or with spray foam (the nonexpanding type is easiest to control).
For an added measure of weather-stripping during cold months, unroll and press in rope caulk where the sash meets the stops, between the top of the lower sash and the bottom of the upper sash, and in the pulley. The window cannot be opened while the caulk is in place, so remove it in the spring.
Test to be sure you will be able to close the window before you apply thick weather-stripping to the underside or top of a sash. To apply self-stick foam, first make sure the surface is clean and dry. Cut the foam with scissors or tin snips. Peel off the backing and press the foam into place.
Cut spring bronze with tin snips to fit precisely. Taking care not to bend the metal as you work, hold the piece in place and drive in the little bronze nails. Drive two or three nails, test to be sure the window will close, then drive the rest of the nails.
For a casement or sliding window, apply V-strip to the side of the sash or jamb for a good seal. Make sure the surface is clean and dry. Cut the V-strip to fit and hold it in position. Peel back the paper as you press the self-stick strip in place.