How to Fix Drafty Windows and Doors

The first cold snap finds the same window every year. You feel the air change a foot before you reach it, and by February you have quietly rearranged the furniture so nobody has to sit there.

Denver’s older housing stock, the 1950s bungalows in Park Hill and Wash Park especially, was never built to today’s air-sealing standards. Air leakage accounts for between 25% and 40% of the energy a typical home uses for heating and cooling, according to ENERGY STAR’s air sealing fact sheet, and most of it escapes through windows and doors.

Cold weather in Colorado arrives fast once it turns. Our full winterization guide walks through the whole seasonal checklist, from sealing to insulation to your heating system, so you’re not tackling one draft at a time. For the quick version, 10 Colorado winter energy tips covers what to do first.

And if you’d rather have a professional map out every leak in your house at once, schedule a home energy audit before the cold really sets in.

What’s Actually Causing Drafty Windows?

Before you fix anything, you need to know where the air is actually getting in. Insulation and air sealing solve two different problems. Insulation works like a sweater. It slows heat from moving through your walls and ceiling. It doesn’t stop moving air. Air sealing works like a windbreaker. Without it, air keeps pushing through every gap it can find, driven by the difference in temperature between inside and outside your home, according to the Department of Energy.

Windows and doors are by far the most common places that difference shows up. Once you have those handled, these are the spots worth checking next:

• Recessed lights and chimney flues
• Your attic access door, covered in more depth in our guide to sealing attic air leaks
• Basement foundation gaps above ground level, and foundation seals
• Outdoor faucets, and anywhere wiring or pipes pass through a wall
• Any seam where two different building materials meet
• Window or wall AC units
• Interior baseboards, mail slots, and pet doors

Our full guide on finding air leaks walks through how to track each one down.

For windows and doors specifically, four tests take a few minutes each, per the Building America Solution Center:

1. The hand test. Run your hand slowly around the window frame on a cold or windy day. You’ll feel the cold air directly.
2. The tissue test. Hold a piece of tissue near the window frame. If it moves or flutters, air is getting through.
3. The nighttime test. After dark, turn on your porch light, then step inside and look at the window frame from indoors. Visible light around the window means air has a path too.
4. The dollar bill test. Close a door or window on a dollar bill. If it pulls out easily, you don’t have a tight seal.

You don’t need a professional to run any of these. A few minutes with your hand, a tissue, a porch light, and a dollar bill will tell you where most of your leaks actually are.

How to Seal Drafty Windows and Doors

Once you’ve found a leak, the fix is usually simple. Sealing and insulating points to two basic moves: weatherstrip your doors and caulk around your windows. Together, sealing air leaks and adding insulation can save up to 10% on your annual energy bill, and it is the cheapest energy efficiency work most homeowners will ever do.

Weatherstripping comes in a few common materials: felt, reinforced foam, vinyl or silicone tape, magnetic tape, and tubular rubber or vinyl. The install steps are the same no matter which one you pick, per the Building America Solution Center:

1. Remove any old, worn weatherstripping.
2. Clean the surface so the new material sticks.
3. Measure and cut your weatherstripping to fit.
4. Install it along the frame.
5. Open and close the door or window to check the fit before you move on.

If your entry door is leaking rather than a window, our guide to weatherstripping your doors walks through door-specific fixes in more depth.

Once the weatherstripping is in, caulk the seams around the window trim to seal gaps in the frame. Caulk works best on gaps smaller than half an inch. It seals irregular gaps more tightly than almost anything else you can buy at a hardware store.

For gaps wider than half an inch, use a backer rod instead of more caulk. And never stuff a gap with loose fiberglass insulation and call it sealed. Fiberglass isn’t an air barrier, so air still seeps right through the fibers, according to lab testing on rough openings.

Weatherstripping, a caulk gun, and a utility knife will get most homeowners through this project in an afternoon. The same tight seal that keeps cold air out in January keeps cool air in come July.

When Caulk Isn’t Enough for Old Windows

Sometimes weatherstripping and caulk don’t fully stop window drafts, especially in old windows. That usually means the leak is deeper: in the rough opening behind the trim, or at the meeting rail on an older double-hung window.

Two quick tests confirm a trim-level leak before you remove anything. 

• The paper test: close the window on a piece of paper and see if it slides out easily. 
• The incense test: hold a lit incense stick near the seam and watch which way the smoke moves. 

Both take about a minute, and together they tell you whether it is worth pulling the trim off at all.

The payoff can be significant. A Building America Solution Center study at Oak Ridge National Laboratory found that a window with a three-quarter-inch unsealed rough-opening gap had an equivalent leakage area of 28.2 square centimeters per square meter. Sealing that gap from the interior side cut it down to 0.5 square centimeters per square meter, a leakage reduction of more than 90%.

For older double-hung windows leaking at the meeting rail, where the two window sashes meet, a removable putty air-sealing cord is a simple seasonal fix, per the Building America Solution Center. More permanent options include interlocking metal strips or silicone gaskets, as long as the lock still opens and closes afterward.

Pulling interior trim is moderate-difficulty DIY work. If you’re not comfortable removing it, it’s reasonable to call a professional rather than force it.

Storm Windows or Window Film?

If the window itself is the problem, not just its seal, no amount of caulk will fix drafty windows for good.

• A few signs point that way, per ENERGY STAR’s window upgrade guide: single-pane glass, a window that leaks air no matter how well it’s sealed, a degraded sill or sash, or a window painted shut.
• Two middle-ground options exist before full replacement. Shrink-to-fit plastic window film is the cheapest and easiest, per ENERGY STAR’s window film guide. It’s a good fit if you notice rattling windows, visible gaps around the trim, dust or pests sneaking in, or peeling paint on the frame.
• Storm windows are a bigger step up. ENERGY STAR’s storm window guide estimates that certified low-e storm windows installed over single-pane glass save homeowners around $350 a year, about 10% on heating and cooling, with a payback period of roughly three years.

For old windows, start with window film if your budget is tight. Move to storm windows if the window sees real daily use and the savings will add up fast. Save full replacement for a window that’s truly failing, not just drafty.

When to Call REenergizeCO

Sealing drafty windows yourself has a real ceiling, and part of the reason is safety, not just effort. A tightly sealed home can trap indoor air pollutants like radon, carbon monoxide, and volatile organic compounds, per ventilation and safety. It can also cause combustion appliances, like a gas water heater, to backdraft. A truly tight home may need extra mechanical ventilation to keep the air safe.

That’s exactly what a home energy audit checks for.

REenergizeCO’s BPI-certified analysts measure your home’s energy efficiency with the full diagnostic stack in one visit: blower door testing, infrared imaging, duct leakage checks, and combustion safety testing. If an auditor skips any of those, it isn’t a complete audit. The visit also confirms your home is still safely ventilated once it’s sealed.

Afterward, you get a report naming the most energy-efficient, cost-effective fixes for your house, ranked in the order you should do them. Because REenergizeCO’s crews are in-house and never subcontracted, the people who found the leak are the ones who come back and seal it.

That’s right! The same crews handle the fixes an audit turns up, from attic insulation to spray foam to crawl spaces, through our home insulation services. If you want to know what audit day looks like first, read how to prepare for your home energy audit or what a blower door test does.