04 / HIDDEN LEAKS
Why is my house so drafty?
Usually one mechanism and four or five holes. Understanding the mechanism tells you which holes to close first.
A drafty house is usually one mechanism and a few holes. Warm air rises and escapes at the top of the house, which pulls cold air in at the bottom — the stack effect. The biggest holes are typically the attic hatch, the garage door, exterior door bottoms, and window frames. Sealing the top of the house is more effective than sealing the bottom.
The mechanism: your house is a chimney
Warm air is less dense than cold air, so the air inside your house is constantly trying to rise. If there is any opening near the top — an attic hatch, a recessed light, a poorly sealed loft door — that warm air leaves. It cannot leave unless something replaces it, so an equal volume of cold air is drawn in through every gap near the bottom of the house.
That is the stack effect, and it explains something people find counterintuitive: the draft you feel at the front door is often caused by a hole in the ceiling. Seal the bottom and the same volume of air still has to come in; it just finds a different way. Seal the top and the whole pump loses pressure.
The causes, in rough order of how much air they move
- 1An unsealed attic hatch or pull-down stair. Frequently the single biggest hole in the building, and almost always uninsulated and unsealed. It sits exactly where the stack effect is strongest.
- 2The garage door. A quarter-inch gap along a sixteen-foot door is a very large opening, and an attached garage is effectively outdoors. See garage seals.
- 3Exterior door bottoms. Visible, easy to fix, and genuinely large. Door sweeps.
- 4Window and door frames — the joint behind the trim. Often open into the wall cavity. Caulk, not weatherstrip.
- 5The fireplace damper. Open or warped, it is a hole to the sky.
- 6Recessed lights and ceiling penetrations. Small each, numerous, and in the worst possible place for stack effect.
- 7Window sashes. The thing everyone blames first, and usually mid-table. Window tape and film.
- 8Outlets and switches on exterior walls. Real, small, easy. Outlet gaskets.
- 9Pipe and cable penetrations under sinks and behind appliances. Small, numerous, cheap to close.
'All of a sudden' usually means something failed
- Weatherstrip has perished. Foam tape in particular takes a permanent set and stops sealing without looking any different.
- The door has dropped. A loose top hinge changes the gap at the latch side by an eighth of an inch, which is enough to notice.
- The fireplace damper has warped or was left open after the last fire.
- A window lock has loosened, so the sashes no longer pull together at the meeting rail.
- Someone has been in the attic and the hatch is not seated the way it was.
- A new extractor fan or dryer vent has increased the depressurization, so existing holes now pull harder.
Where to start, room by room
| What you notice | Most likely | Start here |
|---|---|---|
| Cold air at your feet in a hallway | Stack effect pulling in at the bottom | Door sweeps, then the attic hatch |
| One room always colder | That room's own openings, or missing insulation | Find the drafts |
| Cold near windows | Sash leaks, or radiant loss from the glass | Window sealing |
| The room over the garage is freezing | The garage is effectively outdoors | Garage seals |
| Cold at outlets and switches | Wall cavity connected to attic or rim joist | Outlet gaskets |
| Whole house feels drafty in wind | Many small holes, stack effect | Top of the house first, then the doors |
One thing not to do
Do not seal a house to the point where combustion appliances cannot get air, and do not block deliberate ventilation — trickle vents, extractor ducts, crawlspace vents where they are required. The goal is to close the accidental holes, not the intentional ones. If your house has a fuel-burning appliance and you are sealing aggressively, a carbon monoxide alarm is not optional.
Quick picks
Ranked for fit, not for hype. Tap a row to jump to the full write-up, or go straight to the listing.
| # | Product | Best for | Gap range | Price |
|---|---|---|---|---|
| 1 | Frost King EPDM Rubber Self-Stick Weatherseal Tape, D-Section, 5/16 in x 1/4 in x 17 ftEPDM in a hollow D — the profile that keeps sealing at minus ten where foam tape has already gone hard. | Medium frame gaps | Published 1/4 in thick; compresses to seal gaps of roughly 1/8 in to 1/4 in | CHECK PRICE |
| 2 | Frost King OS6H Foam Outlet and Switch Sealers, 2-1/2 in x 4 inFire-retardant foam gaskets cut to the standard 2-1/2 by 4 inch plate — the part, not a novelty. | The standard outlet gasket | Fits standard US outlet and switch plate openings | CHECK PRICE |
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Medium frame gaps
Frost King EPDM Rubber Self-Stick Weatherseal Tape, D-Section, 5/16 in x 1/4 in x 17 ft
Published gap range
Published 1/4 in thick; compresses to seal gaps of roughly 1/8 in to 1/4 in
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EPDM in a hollow D — the profile that keeps sealing at minus ten where foam tape has already gone hard.
Where the number comes fromFrost King publishes the section dimensions exactly: 5/16" wide by 1/4" thick, 17 ft long. A hollow D seals across roughly half to full its stated thickness, which is where the 1/8-1/4 in working figure comes from.
- Profile
- Hollow D
- Published width
- 5/16 in
- Published thickness
- 1/4 in
- Published length
- 17 ft
- Material
- EPDM rubber
- Mounting
- Self-adhesive onto the door stop
What it does well
- EPDM stays flexible in cold, which is the entire point of a winter seal
- Published dimensions to three fractions — you can actually match it to a measurement
- Compresses without taking a permanent set the way open-cell foam does
Where it fails
- 17 ft is one door frame; a house needs several rolls
- Adhesive still needs a clean, smooth surface
- Thicker than a V-strip, so it can stop a tight door from latching
Who this is forA door stop or window sash with a visible, consistent gap you have measured.
The standard outlet gasket
Frost King OS6H Foam Outlet and Switch Sealers, 2-1/2 in x 4 in
Published gap range
Fits standard US outlet and switch plate openings
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Fire-retardant foam gaskets cut to the standard 2-1/2 by 4 inch plate — the part, not a novelty.
Where the number comes fromFrost King publishes the gasket size (2-1/2 in x 4 in) and that the foam is UL-listed fire retardant plastic. There is no gap range: the gasket seals the plate to the wall, and the leak it stops is the one around the box.
- Published size
- 2-1/2" x 4"
- Material
- U.L. listed fire retardant plastic foam
- Quantity
- 6
- Install
- Behind the faceplate
- Visible after install
- No
- Mounting
- Behind the faceplate, no tools beyond a screwdriver
What it does well
- The fire-retardant rating is the spec that matters on anything going behind a faceplate
- Completely invisible once the plate is back on
- Two minutes per outlet with one screwdriver
Where it fails
- Only helps where the box is genuinely leaking — many are not
- Six per pack does one wall, not a house
- Does nothing about the much larger leaks around windows and doors
Who this is forExterior-wall outlets on the windward side, where you can feel air at the plate.
How we picked
- Explain the mechanism before listing fixes, because the mechanism determines the order the fixes should be done in.
- Rank causes by how much air they typically move, not by how noticeable they are.
We have not tested these products and we do not claim to have. The full method, including what we refuse to claim, is on how we pick.
Ready to locate yours specifically? How to find drafts in your house is the hour-long version with five tests and no equipment.
Questions people actually ask
- Why is my house so drafty all of a sudden?
- Usually something failed rather than something new appeared: perished weatherstrip, a door that has dropped on a loose hinge, a warped or open fireplace damper, a loosened window lock, or an attic hatch left out of position.
- What is the stack effect?
- Warm air rises and escapes through openings at the top of a house, and an equal volume of cold air is drawn in through gaps at the bottom to replace it. It is why sealing the attic hatch often does more for a downstairs draft than sealing the front door.
- Where do most drafts come from in a house?
- In rough order: the attic hatch or loft access, the garage door, exterior door bottoms, the joint behind window and door trim, the fireplace damper, then window sashes, outlets and pipe penetrations.
- Should I seal the top or the bottom of my house first?
- The top. Sealing the bottom alone does not reduce the volume of air moving through the house — it just changes which gap it uses. Closing the high openings reduces the pressure difference driving the whole thing.
- Can a house be sealed too tightly?
- Yes. Combustion appliances need air, and moisture needs a way out. Do not block deliberate ventilation, and fit a carbon monoxide alarm if you have any fuel-burning appliance.
Sources
Every specification on this page traces to a published manufacturer or retailer listing. Where a maker publishes no working gap range, we say so rather than estimating one.
Read next
How to find drafts in your house
Five tests, no equipment, an hour — ordered so you find the big leaks before the small ones.
The best garage door bottom seals
Rubber and EPDM seals by published length and fixing type, plus the case where a bottom seal is the wrong buy.
The best door sweeps, sorted by the gap they actually close
Six sweeps placed by the gap they close, from a slim vinyl blade to a brush for uneven floors.