A blower door test is a method of determining how leaky a building is in terms of air infiltration, or how much cold air leaks into the building during winters and how much warm air leaks out. If the home is being rated from blueprints, the initial rating will assume an infiltration rate. After the home is completed, or for an existing home at the time of the audit, a blower door test is performed to quantify air infiltration and identify where the leaks are located.
A blower door is a calibrated, variable speed fan that is temporarily installed into a door opening using an adjustable frame. It has very accurate manometers that measure the amount of air flowing through the fan. A pressure difference of 50 Pascals is created between the inside and outside of the building. This is equivalent to having approximately a twenty mile per hour wind blowing on all sides of the home. It also simulates the "stack effect" in the home (warm air rising).
The house is depressurized and any leaks (air infiltration) in the home are accounted for through the air being blown out of the door.
By using the volume of the home, the air changes per hour (ACH) is calculated. This number is used, along with the other thermal characteristics of the house, to determine the Energy Rating of the home.