Essentially, a blower door is a very powerful fan that is fixed into the frame of an exterior door. When turned on, the fan pulls all the air out of the house and lowers the air pressure inside. This results in higher outside air pressure flowing into the house through any unsealed cracks and openings, revealing the air infiltration rate of the home and showing where an air leak may be hiding.

Blower doors consist of:

• A frame and a flexible panel that fits into a doorway

• A variable-speed fan

• A pressure gauge that measures pressure differences inside and outside the home

• An airflow manometer and hoses for measuring airflow

• Possible use of a smoke pen to show leakage visually