A blower door is a device used to measure the exact air-tightness of a home.  In the 2015 and 2012-IECC, a maximum air leakage rate is defined and each home must meet this tightness level verified with a blower door test. A blower door is a powerful fan that mounts into the frame of an exterior door. The fan pulls air out of the house, lowering the air pressure inside. The higher outside air pressure then flows in through all unsealed cracks and openings. These tests determine the air infiltration rate of a building. Read our two informative articles, Blower Door Testing and Blower Door Testing for IECC-2012 & 2015.