Finding draughts

You can usually feel a draught but not see where it’s coming from. Cold air travels, so the chill by your chair may start at a gap on the other side of the room. A few minutes spent tracking it down means you seal the right gap first.

Where to look

These are the usual places air gets in. Each links to the guide that covers it.

How to find them

Pick a cold, windy day, when the difference between inside and outside is greatest, and close all the windows and internal doors.

  • Use the back of your hand. It is more sensitive to cold than your palm. Move it slowly round the edges of doors, windows and skirtings.
  • Hold up a strip of tissue or a feather near each likely gap. Wherever it moves, air is moving.
  • Look for light. At night, have someone shine a torch from outside round a door or window while you watch from inside.
  • Try the paper test on doors and windows. Close them on a sheet of paper; if it slides out easily, that edge isn’t sealing.
  • Use a smoke pencil. These give off a thin stream of harmless vapour that bends towards a draught, which shows up small leaks the other tests miss.
  • Use a thermal camera. Low-cost cameras that clip onto a phone show cold spots as blue or purple patches. They work best on a cold evening with the heating on.

For a full picture, a professional air-tightness test uses a fan in an outside door to lower the air pressure inside, then measures how much air leaks in. Testers can use a thermal camera or smoke at the same time to show exactly where it’s getting in. Some retrofit assessments include one.

Draughts and insulation are different jobs

The two are often confused, and both matter.

Draught-proofing stops air moving. Warm air escapes through gaps and cold air comes in through others to replace it. Blocking the gaps stops that flow. The material can be thin, as long as it closes the gap.

Insulation slows heat passing through the fabric of the house: the roof, walls and floors. It works by trapping still air in a thick layer, so thickness matters. The Energy Saving Trust estimates that about a quarter of the heat in an uninsulated home is lost through the roof.

If your loft has little or no insulation, that is usually the first job. After that, draught-proofing is often the cheapest way to make a noticeable difference. Wall and floor insulation cost much more and take longer to pay back. Saving energy covers the other measures.

Before you seal anything

Some gaps are meant to be there. Read Before you start first.

Sources

Last checked 23 October 2026.