How often should you check windows and doors for drafts?

Short answer

Check the windows and doors for drafts once a year, before heating season. A stick of incense held near each frame on a windy day shows where the air comes in, and most of what it finds is fixed with weatherstripping, a door sweep and a tube of caulk. The check takes 30 to 60 minutes for a whole house, and the fixes cost $10 to $40. A professional energy audit, which does the same thing with a blower door and an infrared camera, runs $100 to $300.

Why it matters

Heat leaves a house through the gaps, not the walls. A door with a worn sweep has an opening along the bottom the size of a mail slot, and every window with dried-out weatherstripping leaks around its sash. In winter, warm air flows out through the gaps near the ceiling and cold air flows in near the floor, and the furnace runs to replace what left. The same gaps let cooled air out in summer.

Drafts also carry moisture. Warm indoor air leaking out through a gap in winter condenses inside the wall, which feeds mold and rots framing. Cold air leaking in makes a room feel colder than the thermostat says, so people turn the heat up. Finding and sealing the gaps is the cheapest energy improvement a house can get, and it makes the rooms more comfortable at the same setting.

When to do it more often

The index has no modifiers for this job, so it stays yearly, timed for fall before the heat comes on. Within that, the things that bring a check forward are the ones you feel: a cold spot near a window, a door that lets light through at the edge, or a room that's always colder than the rest. After a renovation that replaced windows or doors, check the new ones in their first fall, since installers don't always seal them well.

What you need

An incense stick or a candle, whose smoke shows the air moving
A flashlight, for looking at seals and sills
Weatherstripping, in the foam or rubber profile that fits the gap
Door sweeps, for the bottoms of exterior doors
Caulk, for the gaps between frames and walls

Steps at a glance

Pick a cold, windy day, turn off the furnace fan, and run the kitchen and bathroom exhaust fans to pull air in through any gaps.
Light the incense and hold it near the edges of each window: along the sash, at the latch, and where the frame meets the wall.
Watch the smoke. If it blows sideways or gets pulled toward the frame, that's a leak.
Do the same at every exterior door, along the sides, the top and the bottom.
At night, have someone shine the flashlight around each door from outside while you look from inside, and mark where light shows.
Replace worn weatherstripping, fit sweeps to doors with light under them, and caulk gaps between frames and walls.

You're done when the smoke rises straight up at every frame and no light shows around any door.

Signs it's overdue

The incense flame or smoke flickers and bends near a frame.
Cold spots next to windows or doors.
Daylight visible around a door's edges.
Higher heating bills than the weather explains.

DIY or pro

This is an easy job with a cheap tool, and the fixes are easy too. Weatherstripping presses into a channel or sticks on, a door sweep screws to the bottom of the door, and caulk fills the rest. Doing the whole house is an afternoon.

A professional energy audit costs $100 to $300 and uses a blower door, a big fan in the doorway that depressurizes the house, with an infrared camera to see where the cold air pours in. It finds the leaks the incense can't, like gaps around plumbing and wiring and in the attic, and many utilities subsidize it. For a house that's drafty even after the windows and doors are sealed, that's the next step.

FAQ

How do you find drafts in a house?

Hold a lit incense stick near window and door edges on a windy day with the exhaust fans running. Smoke that bends or gets pulled toward the frame shows a leak.

What is the cheapest way to stop drafts?

Weatherstripping on windows and doors, a sweep on the bottom of each exterior door, and caulk where frames meet walls. The materials cost $10 to $40 for a house.

Why is my house still drafty with new windows?

The gap between the window frame and the wall may not be sealed, or the leaks are somewhere else: the attic hatch, recessed lights, or holes where pipes and wires pass. An energy audit finds those.

Is an energy audit worth it?

For a house that's drafty after the obvious gaps are sealed, yes. The blower door and the camera find leaks you can't, and the audit costs $100 to $300.