Heated air is less dense than cold air, so houses tested in cold weather appear leakier than they really are (by about 1 percent for each 10 degrees F difference between indoor and outdoor temperature) unless an adjustment for temperature has been made. Otherwise, testing will indicate the amount of less dense air flowing through the blower door, and not the amount of colder, denser air flowing through the holes. From the Journal of Light Construction article: Blower Door Testing by David Keefe, January 2010 issue.
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