In this section
- GuideFind air leaksFour ways to find drafts yourself, from the incense test to a phone thermal camera, and when a blower-door energy audit is worth it.
- GuideWindow filmShrink-film window kits add an insulating air gap to drafty windows. How to install them without bubbles, protect painted trim, and remove them in spring.
Where houses leak
The biggest leaks are usually the ones you can’t see: holes into the attic around light fixtures, pipes, chimneys and the attic hatch, and gaps where the house frame meets the foundation (the rim joist). Windows and doors are next, then outlets and switches on outside walls.
Fixes that work in a rental
None of these is permanent:
- Window insulation film on single-pane or leaky windows. How to install it.
- Removable caulking cord pressed into gaps around window sashes.
- Door sweeps and draft stoppers where you can see daylight under a door.
- Foam gaskets behind outlet and switch plates on outside walls.
- Thermal curtains closed at night in winter.
Fixes for owners
- Weatherstripping on every exterior door and window.
- Caulk and spray foam around pipes, wires and vents that go through walls, floors and ceilings.
- An insulated cover on the attic hatch or pull-down stairs.
- Attic air sealing and insulation. A professional energy audit with a blower-door test shows exactly where the house leaks; some utilities subsidize them.
Don’t seal a house tight around fuel-burning appliances without checking they vent properly. If you have a gas furnace, water heater or stove, a carbon monoxide alarm is a must, and a pro can test combustion safety after big sealing jobs.
Picks
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3M Indoor Window Insulator Kit
Single-pane and drafty windows
- Shrink film and tape
- Removable in spring
Creates an insulating air gap; one of the most effective cheap upgrades for old windows.
Watch for: Test the tape on painted trim first; it can lift paint.
Duck indoor window shrink film
Doing many windows cheaply
- Multi-window packs
- Hair-dryer shrink
Same idea as 3M's kit, often in bigger packs.
Watch for: Same tape caution.
Frost King V-Seal weatherstrip
Sealing double-hung windows and door jambs
- Peel-and-stick vinyl
- Springs into the gap
Closes the gaps where sashes meet the frame, where most window air leaks.
Watch for: Clean the surface well or it peels.
Door sweep for exterior doors
Daylight under the door
- Screw-on or adhesive
- Cut to width
If you can see light under the door, warm air is leaving through it.
Watch for: Measure the gap; sweeps come in different heights.
Foam outlet and switch gaskets
Outlets on outside walls
- Fit behind the cover plate
Outlets on exterior walls leak cold air; a gasket behind the plate stops most of it.
Watch for: Turn off the breaker before removing cover plates.
Mortite caulking cord
Renters: a seal you can peel off
- Putty-like rope
- Removable
Seals window gaps without permanent caulk, so it's lease-friendly.
Watch for: Not for gaps you'll open often.
NICETOWN thermal insulated curtains
Big windows and sliding doors
- Lined, blackout
- Many sizes
Close them at night in winter and on sunny afternoons in summer.
Watch for: Curtains help most when they reach the sill or floor.
TOPDON TC001 thermal camera
Finding the leaks you can't feel
- Plugs into Android phones (USB-C)
- Shows cold spots on walls and windows
On a cold day, drafts and missing insulation show up as dark streaks.
Watch for: Android and PC only; for iPhone, look at FLIR ONE models.
Attic stairway insulation cover
Pull-down attic stairs
- Zips over the opening from the attic side
An attic hatch is often the largest single hole in the ceiling.
Watch for: Measure the opening first.