Trace a Cold Draft at Home With an Incense Stick

Every autumn the same mystery returns to my living room: the windows are shut, the heating is on, and yet a thin stream of cold air brushes my ankles whenever I sit on the sofa. Tracing a cold draft at home feels like detective work, because the air almost never comes from where you first suspect. In my case it was not the window. It was a gap behind the skirting board, two metres away.

Drafts matter more than they seem. Gaps around doors, floors and fittings can account for a noticeable share of the heat a home loses, and they make a room feel colder than the thermostat says. The good news is that finding them needs nothing more than a stick of incense, a quiet evening and a method.

Why a Cold Draft Is Hard to Find

Air leaks follow pressure, not logic. Warm air rises and escapes through gaps high up, in the loft hatch, around ceiling lights and upstairs window frames. That pulls cold air in through gaps low down: under doors, behind skirting, through floorboards. So the cold you feel near the floor may be driven by a hole in the ceiling of the floor above.

There is a second culprit that is not a leak at all. A large, cold window pane cools the air next to it, and that cool air sinks and rolls across the floor. It feels exactly like a draft. If the window frame passes the smoke test below and the cold air only appears on chilly nights, you are probably feeling this downdraft rather than a gap.

The Incense Stick Method

This is the oldest trick and still the best for most homes. A thin, steady line of smoke shows air movement your hand cannot feel.

Pick a cold, windy evening. The bigger the difference between inside and outside, the stronger the airflow.
Close every window and exterior door. Turn off fans and any ducted heating that blows air.
Switch on extractor fans. Run the kitchen hood and bathroom fans on high. They push air out of the house, which pulls outside air in through every gap and makes leaks easier to see.
Move the incense slowly. Hold it a few centimetres from each suspect spot. If the smoke bends sharply or flutters, you have found a leak.

Keep a glass or dish under the stick for ash, and never leave it near curtains. A smoke pencil from a hardware shop does the same job with less mess.

The Usual Hiding Places

When I go through a house with a smoke stick, the leaks almost always turn up in the same handful of spots.

Spot	What to look for
Skirting boards on outside walls	Smoke pulled into the gap between board and floor
Power sockets and switches on outside walls	Smoke pulled into the faceplate edges
Letterbox and keyhole	Strong steady stream, often the worst single leak
Loft hatch	Smoke drawn upward around the edges
Pipes under sinks and behind radiators	Gaps where pipes pass through walls or floors
Unused fireplace	Steady draw up the chimney

Check old window frames too, especially where the sash meets the frame and where the frame meets the wall. Floorboards with wide gaps in older houses can leak along their whole length.

Write each find on a rough floor plan as you go, with an arrow showing which way the smoke moved. Patterns appear quickly. A whole row of leaks along one outside wall usually points to a single cause, such as gaps under the skirting or a floor void open to the outside.

Low-Tech Tools That Help

The back of your hand

Wet the back of your hand slightly and pass it near a suspected gap. Moisture makes your skin more sensitive to moving air. It is quick but misses small leaks.

A sheet of paper

Close a door or window on a sheet of paper. If it slides out easily, the seal is not pressing. Repeat at several points along the edge, because seals often fail at the corners first.

A thermal camera

Phone add-on thermal cameras have become cheaper, and some libraries and energy advice centres lend them. On a cold night they show leaks as dark streaks. Useful, but the incense method finds most of the same problems for almost nothing.

Why You Should Not Seal Every Gap

Once you find drafts, the instinct is to block every one. This is where common advice goes wrong. Homes need controlled ventilation. Window trickle vents, air bricks and vents in rooms with gas appliances are there on purpose. Blocking them can lead to condensation, mould and, in rooms with a boiler, fire or stove, a real safety risk from poor combustion air.

The rule I follow is simple: seal accidental gaps, keep designed vents open. Gaps behind skirting, around pipes and under doors are accidental. A grille in the wall or a narrow vent at the top of a window frame is designed. If you are not sure, ask a heating engineer before covering it. A damp, sealed house can create a new mystery, as anyone who has tried tracking down a mystery smell after a renovation knows.

Cheap Fixes for What You Find

Most draft fixes cost less than a takeaway meal and take an afternoon.

Clear decorator's caulk or flexible sealant along skirting gaps and around pipes.
Foam or brush strips on door frames, and a brush strip or draft excluder at the bottom of exterior doors.
A letterbox brush and a keyhole cover.
Foam gaskets behind socket faceplates on outside walls, fitted with the power switched off at the fuse box.
Self-adhesive seal around the loft hatch, plus a latch so it presses shut.
A removable chimney balloon or draft stopper for an unused fireplace, taken out before any fire is lit.

Afterwards, watch the next energy bill. If it still climbs, our guide to finding what is raising your electricity bill covers the other usual suspects. More home puzzles live in the living section.

Draft Hunting FAQ

Can I find drafts in summer?

It is harder, because there is little temperature difference. Running extractor fans helps, but a cold, windy evening gives much clearer results.

Is incense safe to use near sockets?

Yes, the smoke is harmless to sockets. Keep the glowing tip away from fabric and paper, and never leave it unattended.

Why is one room colder even with no drafts?

Probably the window downdraft effect, or poor insulation in that room's outside wall or floor. Heavy curtains that reach the sill or floor often help.

Tonight's Draft Hunt

Wait for the next cold, windy evening, close everything, switch on the extractor fans and walk each outside wall with an incense stick. Write down every spot where the smoke moves, sort them into accidental gaps and designed vents, and fix only the first group. One evening of detective work can solve a mystery that has been chilling your ankles for years.