How to fix drafty windows before winter

As winter gets close, you walk past a window and feel cold air coming in around it. It is a common thing to find in a house, and most of the time you do not need a new window to stop it.

There are four ways to fix a drafty window: caulk, weatherstripping, plastic film, or a new window. Which one you need depends on where the air is getting in, so the first job is finding that out before you buy anything.

• Caulk goes on the parts that never move: the joint where the window frame meets the wall, and the gaps around the trim.
• Weatherstripping goes on the parts that do move: the sash you slide up and down, and the spot where the window closes against the frame.
• Plastic film is a cheap fix for one cold winter. It does not repair anything, but it stops the draft you feel tonight.
• A new window is for a window that is actually broken, like wood that has rotted, a sash that will not close, or glass that has fogged up between the panes. It is not something you buy because a salesman says your bills are high.

The sealing work is worth an afternoon of your time. The Department of Energy says sealing uncontrolled air leaks can save 10% to 20% on your heating and cooling bills, and it lists caulking and weatherstripping as the quickest of those jobs. ENERGY STAR puts air sealing plus insulation at up to 10% off a yearly energy bill. A new window costs thousands of dollars, and a tube of caulk costs a few.

How to find where the draft is coming from

A draft near a window is not proof the window is bad. The air could be coming in around it, through a gap behind the trim, and that is a different repair with a different price. So it is worth checking before you buy anything.

Look for the easy signs. ENERGY STAR lists the ones to watch for: a draft you feel when the window is closed, gaps you can see around the trim, dust or bugs coming in, outside smells, and paint peeling around the frame. I would add one more to that list. If you can see daylight around the frame, you are looking at a hole, and air goes wherever light goes.

Do the paper test. ENERGY STAR says to close the window on a piece of paper. If the paper slides back and forth easily, the window is not closing tight, and thicker weatherstripping is the answer.

Do the smoke test. Pick a windy day. The Department of Energy says to carefully hold a lit incense stick or a smoke pen next to the window, and that if the smoke stream travels sideways, you have found an air leak. Move it slowly along the sash, then along the joint where the frame meets the wall. Where the smoke bends is where the air is moving.

Where the smoke bends tells you which fix you need. If it bends at the sash, the window needs weatherstripping. If it bends at the edge of the frame or the trim, that gap needs caulk. If the smoke stays straight everywhere but the glass is still freezing cold to the touch, the glass itself is losing the heat, and that is the film-or-replace question at the end of this post.

If the whole house feels drafty and you cannot tell why, that is bigger than a window. The Department of Energy says a do-it-yourself hunt works fine for obvious leaks around window and door frames, but not for the small hidden ones, and that a certified energy assessor uses a blower door and an infrared camera to find those.

Caulk the gaps around the frame and the trim

Caulk is for cracks between parts of the house that hold still. Weatherstripping is for the parts that move. The Department of Energy’s air sealing guide splits its material list the same way, with caulk and spray foam for cracks and openings, and weatherstripping for places like the joint between a window frame and its sash.

The size of the gap decides what you use. ENERGY STAR says caulk handles gaps of a quarter inch or less. For anything bigger, use a non-expanding foam sealant made for windows and doors, or push in backer rod first and then caulk over it. Do not jam the backer rod in hard. ENERGY STAR warns that forcing it can bend the frame just enough that the window stops opening right.

Clean the crack out before you caulk it, and smooth the bead with your finger so it really seals.

What about a big gap right next to the window?

That one usually is not the window at all. It is the space between the window jamb and the rough opening in the wall, and it was supposed to be sealed and insulated before the trim went on.

ENERGY STAR walks through pulling the interior trim off to look. If you find little or no sealant back there, it says you have probably found the same problem at every window in the house. Fill it with non-expanding foam, fiberglass, or backer rod, then put the trim back.

Two warnings before you pry anything. Most homes built before 1978 have lead paint, and cutting or prying painted trim makes dust you do not want to breathe. The EPA’s lead renovation program explains what to do about that. And if your trim has sills or decorative pieces, ENERGY STAR says to let a pro take it off.

Weatherstrip the parts of the window that move

If the paper test failed, this is your fix. The sash is not sealing against the frame, and no amount of caulk will help, because caulking a moving part glues your window shut.

The Department of Energy lists the kinds made for this, including the ones that go between window frames and sashes: tension seal, felt, reinforced foam, rubber tape, bulb or fin seals, and interlocking metal channels. The product aisle is confusing, so bring a photo of the gap and match the shape.

Old windows have one more hiding spot. ENERGY STAR notes that older double-hung windows have hollow cavities in the wall for the counterweights, and those can be sealed. If the ropes and pulleys still work, little plastic pulley seals close the holes without killing the window.

There is one free thing to try first, which is to lock the window. On a double-hung, the lock pulls the two sashes together, and that is sometimes enough to close the gap the air is coming through.

Is plastic window film worth it?

For the right window, it is worth it. A twenty dollar film kit is the cheapest fix in this whole post.

ENERGY STAR rates a shrink-film kit as an easy, one-day project under $100, and says the film cuts drafts, makes the room feel warmer, and reduces the water that collects on cold glass. It says the film can even stop the air leaks around the window when you run it out over the woodwork, because the plastic traps a layer of still air in front of the glass.

A kit is film and double-sided tape. You clean the frame, tape the film on, and shrink it tight with a hair dryer. ENERGY STAR says to take it down when winter is over, and that the tape comes off without hurting the finish.

I should be honest about what film is, though. It is a cover, not a repair. The gap behind it is still there in April, and you cannot open that window until you pull the plastic off. So I use film on the windows I do not open in winter anyway, and I still caulk the gap when the weather warms up.

If you want the same idea in a permanent form, storm windows are the step up. The Department of Energy says low-e storm windows, inside or out, can save 10% to 30% on heating and cooling, depending on the window you already have.

When it is time to replace the window

Replace the window when the window itself is the problem. That means soft or rotted wood, a sash that will not close or lock, cracked glass, or glass that looks foggy or has water between the panes. Foggy glass means the seal between the panes has failed, and that is not something you can fix with a caulk gun.

Everything else deserves a seal attempt first. The Department of Energy says to be sure you have already air sealed and insulated your home before you replace your windows.

The savings are real, and they are also smaller than the sales pitch. That same guide puts new ENERGY STAR windows at 7% to 15% off a yearly household energy bill, depending on where you live and what you are replacing. ENERGY STAR says up to 13% nationwide when you are replacing single-pane windows. The Department of Energy also says homeowners get back about 78% of the cost when the house sells, and that new windows can carry a long payback period.

Two things to hold onto if you do buy. That window guide warns that even the most efficient window can leave you with a drafty, sweating house if it is not installed properly, and the Energy Saver guide says to have windows installed by trained professionals following the maker’s instructions, or the warranty may be void. A window quote is also not an emergency, so get a second one and a third before you sign anything. How to tell if a contractor quote is fair is what I do once I have more than one number in front of me.

Write down which windows you sealed and when

Caulk does not last forever, weatherstripping wears out, and next October you will not remember which three windows you did and which five you ran out of daylight on. Written notes also tell you what to try next. A window you already caulked that is still drafty a year later is asking for weatherstripping, not for more caulk, and the only way you know it was caulked is because you wrote it down.

So keep four things per window: which window, what you did, the date, and what you noticed but did not fix.

Tobi’s maintenance log is where mine lives. The windows go in as their own record in the home, and the fall check is a recurring task on that record, so it comes up due every year instead of waiting on my memory. Marking it done leaves a line in the history with the date, who did it, and notes for that one time. Nothing gets written over, so three years reads as three passes around the house.

Everyone in the household sees the same record in real time, on their own iPhone or iPad, or on an Apple Silicon Mac. The person who feels the draft is not always the person who fixed it last time. If a window company does the work, they go in as a contractor, and the job keeps their name on it.

The fall window check belongs on the same short list as the gutters and the furnace filter. The home maintenance schedule that actually survives real life is the rest of that list.

What I do every fall

I wait for a windy, cold-ish day and walk the house with an incense stick.

Smoke that bends at the sash gets weatherstripping, smoke that bends at the frame gets caulk, and any gap wider than a quarter inch gets foam before I caulk over it.

The two windows that are still cold after all that get a film kit, because they are the ones nobody opens in January anyway.

Then I write down what I did, window by window. That takes two minutes, and it is the reason next fall is a short job instead of a mystery.