How to find drafts in your house

You do not need a thermal camera. Every test below uses something already in the house, and together they find the leaks that matter on almost any home. What they will not do is find leaks inside the wall structure — for that you need a blower door and someone who does this for a living.

First, tilt the odds: depressurize the house

1. 1Close every exterior window and door.
2. 2Close the fireplace damper if you have one.
3. 3Turn off the furnace or any combustion appliance, so you are not fighting its air supply.
4. 4Turn on the bathroom extractor fans and the kitchen range hood.
5. 5Leave them running. The house is now slightly below outside pressure and every gap is pulling air inward, which makes all five tests dramatically more sensitive.

Test 1: the hand test (finds the big ones)

Wet the back of your hand slightly and move it slowly along the edges of doors and windows, an inch or two from the surface. The back of the hand is far more sensitive to moving air than the palm, and damp skin more sensitive than dry. Anything you can feel this way is a large leak and should be fixed first.

Test 2: the incense test (finds most of the rest)

1. 1Light an incense stick, or a match blown out so it smokes.
2. 2Hold it two or three inches from the surface you are testing and watch the smoke column, not the stick.
3. 3A vertical column means still air. A column that bends sideways or breaks up means air movement.
4. 4Work systematically: door frames, window frames, the attic hatch, baseboards, outlets on exterior walls, and where pipes enter under sinks.
5. 5Mark every hit with masking tape and keep going. Sorting comes later.

Test 3: the dollar-bill test (finds bad seals)

Close a door or window on a dollar bill and pull it out. If it slides freely, the seal is not compressing at that point. Do it at eight or ten points around each opening — you get a map of where a seal has failed, which the smoke test does not give you as precisely.

Test 4: the flashlight test (finds daylight gaps)

After dark, have someone shine a strong flashlight around the outside edges of a door while you watch from inside with the lights off. Anywhere the light shows through is a direct hole. This is the fastest way to check a garage door, where the gaps are large enough to see and awkward to reach with smoke.

Test 5: the touch test (finds insulation gaps)

On a cold day, put your palm flat on interior walls and ceilings in the rooms that feel worst, especially the ones backing onto an attic, a garage or an outside corner. A patch that is noticeably colder than the wall around it is missing insulation rather than leaking air — a different problem, worth knowing about, and not one that weatherstrip will fix.

Now sort what you found, biggest first

The two places most people never check

The attic hatch. A plywood panel resting in a frame with no seal, at the top of the house where warm air is trying hardest to escape. Smoke-test its edges with the fans running and you will usually see the column move decisively. A perimeter bulb seal and something heavy or latched to hold it down is the fix, and it is one of the highest-value hours in this whole list.

The fireplace. An open damper is a permanent hole to the sky. Check yours actually closes, and closes fully — dampers warp, and a warped damper is a chimney-sized leak. If the fireplace is not in use at all, a chimney draft stopper is a genuine fix, provided you leave an unmissable reminder that it is up there.

Both of these get their own dedicated sections on this site later this year. For now, smoke-test them and deal with the doors, windows and garage — which on almost every house are the bigger numbers anyway.