The blower door is my No. 1 tool when diagnosing air leakage problems in a building. This tool not only gives me an idea of how leaky the building is, but also indicates the location(s) of the air leaks. There are several ways this can be done but my go-to method is a thermal imaging camera. These cameras help get a good visual of temperature differences that can be created during blower-door testing—that is, if there is a temperature difference between inside and outside the home. If there isn’t, then thermal imaging won’t work.

Your senses can be a useful tool too. Look for moving curtains or cobwebs; keep a nose out for the smell of raw fiberglass; listen for a whistling sound, which can indicate air moving through a hole; and use the back of your hand to feel for air leaks.

Using smoke to find holes in the building envelope is yet another effective method and the focus of this post.

Four types of testing tools

I own four different tools that can produce smoke: a smoke pen, a smoke puffer, and two different theatrical foggers. The smoke pen is a simple test tool used to pinpoint air leaks. It has a wick that is lit on fire with a lighter or match. Once the wick has burned for a few seconds, you blow out the flame and allow the wick to smoke. The smoke lasts only a few minutes; when the the pen stops smoking, you will have to re-light the wick. This tool is cheap and reliable but you have to work with an open flame, which can be hazardous in tight spaces like an attic or crawlspace.

A better option for spot-testing…