What does a blower door do? Solution A blower door is a device which is used to measure the air tightness of buildings. It is also used to find out the air flow in between the building zones, to test duct network air tightness and aslo to physically locate air leakage sites n the building envelope.There are 3 primary components of blower door. They are: 1)calibrated variable speed fan 2)pressure measuring instrument 3)mounting system.