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Locating Building Air Leakage Using Infrared Thermography

We now know that adequately insulating buildings, while essential, is only part of what is required to minimize the energy use and maintain comfort. Buildings also leak air, typically three or more times than is useful, and most kinds of insulation don’t necessarily control it. Excessive air leakage can also cause moisture problems and, in cold climates, costly frozen water pipes!

Thermography allows us to see the airflow pathways across and through the building envelope. While it is possible to detect these with our imagers under natural building pressure differences, it is usually far more useful to control and enhance the air movement using a blower door.

Under natural conditions, buildings behave like chimneys—a phenomenon called the “stack effect.” In a heated building, warm air leaves (“exfiltrates”) the upper parts and cool air comes in (“infiltrates”) the lower parts. An air-conditioned building is also subject to natural air leakage, but it may be less predictable. When the wind blows, the resulting pressure plane skews these natural patterns, causing air to exfiltrate downwind and infiltrate on the windward side. Understanding these often complex variables is not easy!

Warm air leaking out of the walls of this older home leaves a classic thermal signature on the eaves.

However, a blower door will simplify your life as a thermal imager owner. By depressurizing a home—to a 10-20 pascal gradient with a temperature difference of 3C-10C (5F-18F)—we begin to see the effects of air leakage from the interior. Direct leakage shows up immediately and dramatically, while indirect pathways may be more subtle and slow to reveal themselves. Essentially, any changing thermal pattern is a result of air leakage. While the use of the blower door is simple, it should not be done without proper training.

A blower door is an essential part of using thermography to fully understand air leakage.

Air leakage testing using thermography and a blower door has long been part of an audit.  However, nowadays, both are commonly used during the installation of air sealing materials as well as at the “testing out” stage—which is a great way to fix the problem before it even starts!

Stay tuned for next week’s posting, focusing on roof moisture!

Thinking Thermally,

John Snell—The Snell Group, a Fluke Thermal Imaging Blog content partner

3 comments to Locating Building Air Leakage Using Infrared Thermography

  • This blower door looks very fragile :/

    So once you decreased the pressure in the building, did you remain inside and do an internal thermal imaging survey, or only from the outside?

  • The blower door is actually very rugged. The adjustable fabric door is made of a heavy rip-stop nylon type material while the frame is aluminum. Other brands of door have adjustable plastic panels and either type can work very well. Once the door is in place the fan is set to depressurize (typically) the building and all work is done from the interior where we see the air infiltrate from the outside. I would encourage you to find someone who can demonstrate this to you. It is really impossible to fully understand a building without manipulating the air flow rate and direction and in most cases a blower door is the easiest way to do that.

  • I just finished the blog. Really very helpful. Thanks for sharing such an amazing blog.
    Tacoma Roofing

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