Blower Doors assist in locating air leaks in houses by inducing air infiltration or exfiltration. The blower door exaggerates existing air leakage paths making them easy to locate with a smoke generator, infrared camera or simply using your fingers. Building leakage associated with forced air system ductwork can also be found through blower door diagnostics.

The blower door consists of a powerful variable speed fan that is sealed into an exterior doorway and is used to blow air into or out of a house. When air is blown out of the house, it causes a slight negative pressure (or vacuum) in the house relative to outside. This negative pressure induces outside air to enter the house (infiltration) through cracks or holes found in any exterior house surface. The blower door can also be used to pressurize the house by blowing air into the house and creating a slight positive house pressure relative to outside. In this case, the positive pressure induces household air to escape (or exfiltration) through holes or cracks in the structure.