Winter Draft-Proofing Guide: Windows, Doors and the Leaks That Cost You Money

Draft-proofing a typical US home costs $200 to $600 in materials, takes a weekend, and cuts heating bills by 10 to 20 percent — about $150 to $400 a year — because air leaks around windows, doors, attics and foundations waste more heat than a thin wall ever will. Find the leaks first with a candle or an incense stick on a windy day, seal the big leaks in the attic before the small ones at the windows, and work top to bottom. Check your insulation levels with the Insulation Calculator, measure the rooms you are sealing with the Square Footage Calculator, compare insulation costs in the insulation cost guide, and fold the work into the winter home maintenance checklist so it is done before the first hard freeze.

Finding the leaks: the test that shows you where the money goes

Find air leaks with a candle or an incense stick on a windy day, because the leaks you can feel are only the worst ones — the leaks that cost the most money are the ones you cannot feel. Close all the windows and exterior doors, turn off the furnace and any exhaust fans, then light an incense stick and hold it slowly around the edges of windows and doors, electrical outlets on exterior walls, recessed lights, the attic hatch, the basement rim joist, and where pipes and wires pass through walls. Smoke that wavers, bends sideways or is sucked toward a gap marks a leak; smoke that rises straight up marks a sealed joint. Do the test on a day when the temperature difference between inside and outside is at least 20°F (11°C), because the stack effect — warm air rising and escaping through the top of the house while cold air is pulled in at the bottom — is strongest then, and the leaks show up most clearly. A blower-door test from an energy auditor ($300 to $500) measures the whole house in one number, air changes per hour at 50 pascals, and a typical older US home tests at 7 to 10 air changes per hour while a tight new home tests at 2 to 3 — the test also comes with an infrared scan that shows the leaks as cold spots, which is worth the money if you are planning a larger insulation job.

Expect the biggest leaks to be where you least expect them. The attic hatch and the attic access stairs leak more air than all the windows in the house combined in many homes, because the hatch is a large unsealed hole at the very top of the stack effect, and a 2 ft by 2 ft (61 cm by 61 cm) hatch with a 1/8 in (3 mm) gap around it leaks as much air as a 2 in (5 cm) hole drilled straight through the ceiling. Recessed lights are the second surprise: each non-airtight recessed light leaks as much air as a 1 in (2.5 cm) hole, and a house with 20 of them has the equivalent of a 6 in (15 cm) hole in the ceiling. The basement rim joist — the band of wood where the floor framing sits on the foundation — is the third: it is the largest single air-leak area in most basements, it is usually completely unsealed, and it is also where cold air pours in at the bottom of the stack effect. Windows and doors, the leaks people think of first, are typically only 10 to 15 percent of the total air leakage in an older home — which is why sealing windows first and ignoring the attic is the most common draft-proofing mistake.

Prioritize the work in this order, because the order determines the payback: first the attic — the hatch, the recessed lights, the plumbing and wiring penetrations, and the top plates of interior walls; second the basement rim joist and the sill plate; third the exterior doors; and fourth the windows. The attic and basement leaks are the big holes at the top and bottom of the stack effect, and sealing them changes the pressure balance of the whole house, which reduces the draft through every window and door at the same time. A homeowner who seals only the windows saves 3 to 5 percent on heating; a homeowner who seals the attic and the rim joist first saves 10 to 20 percent, and the window sealing after that is the finishing touch rather than the main event.

Windows: weatherstripping, caulk and the fixes that actually work

Seal windows with the right product for each joint, because caulk and weatherstripping do different jobs and using one where the other belongs wastes both. Caulk seals joints that never move — the gap between the window frame and the wall, the gap between the trim and the wall, and any crack in the frame itself. Use silicone or siliconized acrylic caulk ($5 to $10 per tube) for exterior joints, because it stays flexible in cold weather and lasts 10 to 20 years, and paintable acrylic latex caulk for interior joints that will be painted. Cut the tip to match the gap, push the caulk into the gap rather than laying it on top, and tool it smooth with a wet finger within 5 minutes — caulk that sits on top of a gap instead of in it peels off in the first winter. Weatherstripping seals joints that move — the sash meeting the frame, the meeting rail where the two sashes overlap, and the bottom of a sliding window. For a double-hung window, V-strip (spring bronze or vinyl, $5 to $15 per window) on the sides of the sash and a foam or felt strip on the meeting rail works best; for a casement window, a compressible foam or rubber bulb seal around the frame works best, because the sash presses against it when it closes.

Replace weatherstripping when it is compressed, cracked or missing, and test the seal with a dollar bill: close the window on a dollar bill and try to pull it out — if it slides out easily, the seal is gone and the weatherstripping needs replacing. A window that rattles in the wind has lost its weatherstripping and is leaking badly; a window that is hard to close has weatherstripping that is too thick, which is almost as bad, because a window that does not close fully does not seal at all. For windows that are single-pane or that have failed seals (fog between the panes means the seal is gone and the insulating gas has escaped), the honest fixes are a storm window ($100 to $300 per window installed, which adds an insulating air layer and cuts heat loss by 25 to 50 percent) or a window insulation film kit ($5 to $15 per window, a clear plastic sheet shrunk tight with a hair dryer that adds an insulating air layer for one winter). Film is the cheapest fix that actually works and is the right answer for a rental or a window that will be replaced in a year or two; a storm window is the right answer for a window that will stay for five years or more. Never seal a window shut with caulk if it is an egress window or the only window in a bedroom — a sealed-shut bedroom window is a fire safety hazard and a code violation.

Check the window frame itself, because a window with a rotten sill or a cracked frame leaks no matter how good the weatherstripping is. Probe the sill and the bottom of the frame with a screwdriver: wood that is soft, crumbly or that the screwdriver sinks into is rotted and needs repair ($150 to $400 per window for a sill replacement) or replacement. A window that has been painted shut is not a sealed window — it is a window that cannot be opened for ventilation or escape, and it should be freed with a utility knife and a putty knife, not left painted shut. And do not forget the window lock: a double-hung window that is not locked leaks more air than a locked one, because the lock pulls the two sashes together and compresses the weatherstripping at the meeting rail — the simple act of locking every window in the fall is free draft-proofing that most households skip.

Doors, attic and basement: the leaks that pay back fastest

Seal exterior doors with a door sweep and weatherstripping, because a 1/8 in (3 mm) gap under a 36 in (91 cm) door leaks as much air as a 2 in (5 cm) hole in the wall. A door sweep ($10 to $25) screws or sticks to the bottom of the door and seals the gap to the threshold; a door shoe ($15 to $30) does the same job and lasts longer because it replaces the bottom edge of the door rather than hanging below it. Weatherstrip the sides and top with a foam, felt or rubber bulb seal, and test the seal with the dollar-bill test at the top and sides as well as the bottom. If daylight is visible around a closed door, the door is leaking badly — adjust the strike plate and the hinges first, because a door that does not close squarely cannot seal no matter how much weatherstripping you add, and a door that has settled on its hinges can often be fixed by tightening the hinge screws or replacing one short screw per hinge with a 3 in (76 mm) screw that bites into the framing. A storm door ($200 to $600 installed) adds an insulating air layer and protects the main door from weather, but it is not a substitute for sealing the main door — a storm door over an unsealed main door is two leaky doors instead of one.

Seal the attic hatch with an insulated cover, because a bare plywood hatch is an uninsulated hole at the top of the house. Glue 2 in (5 cm) of rigid foam to the back of the hatch (R-10), add weatherstripping around the opening, and add a latch or a weight that holds the hatch tight against the seal — a hatch that sits loose leaks as much as a hatch with no weatherstripping at all. For pull-down attic stairs, buy a pre-made insulated stair cover ($100 to $250), which is a zippered tent of foil-faced insulation that sits over the stairs and seals the opening, or build one from rigid foam board and foil tape for $40 to $80. Seal the plumbing and wiring penetrations in the attic floor with fire-rated caulk or expanding foam ($5 to $15 per can) — every pipe, wire and duct that passes through the ceiling is a hole, and a typical house has 20 to 40 of them, each leaking a little air that adds up to a lot. Cover non-airtight recessed lights with an airtight, insulation-contact-rated box ($10 to $20 per light) or replace them with airtight LED retrofits ($15 to $30 per light), and never bury a non-rated recessed light in insulation, because it is a fire hazard — the light needs air to cool, and insulation around it traps the heat.

Seal the basement rim joist with rigid foam and caulk, because it is the largest single air-leak area in most basements and the fix is a weekend job that pays back in one winter. Cut rigid foam board (2 in, or 5 cm, extruded polystyrene, R-10) to fit each joist bay, glue or friction-fit it against the rim joist, and seal all four edges with caulk or expanding foam — the foam board is the insulation and the caulk is the air seal, and both are needed, because foam board without sealed edges leaks air around the edges and caulk without foam board insulates nothing. A basement rim-joist job costs $100 to $300 in materials for a typical house and saves $100 to $300 a year in heating, which is a payback of one to two years — the fastest payback of any draft-proofing job. Seal the sill plate (where the house framing sits on the foundation) with a bead of caulk along the inside joint while you are there, and seal around any pipe or wire that passes through the rim joist with expanding foam. Wear gloves and eye protection when cutting foam board, and cut it outside or with a vacuum, because the dust is irritating and the offcuts are a mess indoors.

Costs, savings and the weekend plan

Budget $200 to $600 in materials for a whole-house draft-proofing job: $50 to $100 for caulk and weatherstripping, $50 to $150 for a door sweep and weatherstripping set per exterior door, $100 to $250 for an attic stair cover, $100 to $300 for rim-joist foam and caulk, and $20 to $50 for window film kits if needed. A professional air-sealing job costs $1,000 to $3,000 and includes a blower-door test before and after, which is worth it if the house is large, old, or has a finished attic that is hard to access. The US Department of Energy estimates that air sealing plus insulation saves 15 percent on heating and cooling costs on average, and 10 to 20 percent is a realistic range for a leaky older home — $150 to $400 a year for a typical household paying $1,500 to $2,500 a year for heating. The payback on a DIY job is one to three years, and the comfort payback is immediate: the cold draft by the sofa, the cold floor by the front door, and the bedroom that never warms up are usually air leaks, not heating problems, and sealing them fixes the comfort problem the thermostat never could.

Do the job in one weekend, in this order: Saturday morning, the incense test to find the leaks and a shopping list from what you find; Saturday afternoon, the attic — hatch, penetrations, recessed lights — because it is the worst job and it is best done while you are fresh; Sunday morning, the basement rim joist and sill plate; Sunday afternoon, the doors and windows, working room by room with the caulk gun and the weatherstripping. Keep the house ventilated while you work, especially when using expanding foam, and do not seal a house so tight that it has no fresh air: a house sealed below 3 air changes per hour at 50 pascals needs mechanical ventilation (a heat-recovery ventilator, $1,500 to $3,000 installed) to keep indoor air healthy, because a house that cannot breathe traps moisture, cooking fumes and radon. Most older homes will not get that tight from a weekend of sealing, but a home that has been fully air-sealed and insulated should have its ventilation checked — and a carbon monoxide detector on every floor is a safety item that matters more, not less, as a house gets tighter.

Mistakes and the final checklist

Avoid the mistakes that waste a draft-proofing weekend: sealing the windows first and ignoring the attic and rim joist, caulking a joint that moves, weatherstripping a joint that never moves, sealing a bedroom egress window shut, venting a bathroom fan into the attic while sealing the attic floor (the fan moisture then has nowhere to go), and using expanding foam around a window or door frame, where it bows the frame and jams the sash — use low-expansion foam made for windows and doors, or backer rod and caulk, for those joints. Add one more: sealing the attic floor without checking that the bathroom and kitchen fans vent outside first, because an airtight attic floor with a fan venting into it traps warm moist air in the attic, which condenses on the cold roof and rots the sheathing. Check the fans before you seal, not after.

Run this final checklist before the first hard freeze: every window locks and passes the dollar-bill test, every exterior door has a sweep and weatherstripping with no daylight visible around it, the attic hatch is insulated and latched tight, the rim joist is foamed and caulked, the recessed lights are covered or replaced, and the furnace filter is clean, because a clean filter is the heating-system equivalent of draft-proofing — a dirty filter makes the furnace work harder for the same heat. Then check the heating bill in January against last January, adjusting for how cold the month was: a 10 to 20 percent drop in a month of similar weather is the proof the work paid off, and it is the number that makes the next draft-proofing weekend — the one that adds attic insulation on top of the air sealing — an easy decision.