The Blower Door is a diagnostic and measurement tool designed to provide two basic functions for weatherization and building professionals:
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.
Blower Doors measure and quantify the airtightness of house. This measurement allows us to determine the effectiveness of weatherization activities and new construction techniques, and provides a means for estimating the natural infiltration rate of the house helping to assure that the building has adequate ventilation.
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.
Blower Doors use gauges that allow us to measure both the pressure difference between inside and outside of the house ( or house pressure differential), and the amount of air flowing through the fan. Pressures measured by the blower door gauges are in a metric unit called the Pascal (or Pa). The flow rate through the calibrated blower door fan is measured in cubic feet of air per minute (or CFM). A common blower door measurement used by weatherization professionals is the fan flow which is needed to create a constant house pressure differential of 50 Pa. This flow at 50 Pa typically ranges between 500 and 8000 depending on the leakiness of the house being tested.