Detecting Air Leaks

How to identify the source of drafts in your home.

There are a number of ways you can detect air leaks in your home, whether they're around windows, doors, attic hatches, or pipes and wires. These work best on a cold and windy day. That doesn't mean you can't test for leaks in summer—it's just a bit more work.

A few things to keep in mind before testing for air leaks.

  • Turn off fans, furnace, or air conditioning.
  • Take a roll of rope caulk and see if you can fix the leaks as you go.
  • A combination of the techniques below should identify most air leaks. Incense seems to be the easiest and most effective of them all.
Technique Description How Effective
Wet Hand Simply dampen your hand and hold it near where you suspect air is leaking. If cold air is coming in you'll feel it. Works well when cold air is entering the house; not as well if air is escaping.
Look For the Light At night have someone shine a light around the suspected air leak from outside. If you can see the light coming through, you've found your problem. Very effective for walls and around pipes entering the house. Not as useful for windows.
Incense Hold smoldering incense near the area of concern. Watch the motion of the smoke. Use a small flashlight to make the smoke easier to see.
Incense Rising in Room
Effective and can help find air entering or exiting the house. Tough to see against white backgrounds (you can put a piece of black paper off to one side for contrast). Incense rising near a leaky window.
Plastic Wrap Tape a one-inch-wide strip of thin plastic wrap to a pencil. Hold in front of suspected air leak. Several strips of Christmas tree tinsel also work well. Not as sensitive as incense but useful for detecting many drafts, especially on windy days.
Candle Don't do it. You'll burn your house down. Again, curtains on fire and such.
Baby Powder Shake the baby powder container and puff a bit of powder in the air. Watch to see the movement of the powder. Not quite as good as incense but still effective. It takes some practice to get the powder to puff out evenly.
Thread For bigger leaks, you can tape a small piece of thread near where you suspect the leak and watch for moment. It won't be as dramatic as incense smoke. Okay for bigger leaks or on a windy day.
Blower Test (do–it-yourself) Close all windows and doors. Turn on all exhaust fans. Put a window fan in a window blowing air out of the house. Use one of the techniques above to see where air is entering the house. Works reasonably well to identify air leaks. Combine with the techniques listed above to find the leaks. Can be used in summer.
Blower Test (professional) It's the same idea as you doing the blower test but they have a bigger fan that fits, airtight, onto your front door. This provides a stronger pull and leaks are easier to see. It's not a bad idea to try to deal with the major leaks yourself before having a professional blower test done.

Probably the best approach is to identify and fix the biggest air leaks using the wet hand technique or incense/baby powder. After you've done that, a do-it-yourself blower test will be more effective at finding the remaining leaks. If you still believe there to be a problem you can have a professional blower test done.