Weatherization experts, those friendly folks that insulate and air seal homes, have developed several tools to aid them in diagnosing air leakages in a home. A blower door test is just such a diagnostic tool; this specific test artificially creates a vacuum between your home and the outside, which causes a pressure difference between the two areas. To begin the test, the weatherization technician will first close all exterior doors and windows in the home and will then set up a large fan in the front door of the house. This fan faces outside and is sealed on all sides to the edge of the door with small hoses running both outside and inside to measure the air pressure. When the fan has created a pressure difference of 50-pascals in cubic feet per minute (CFM) the airflow through the fan is then measured. This number can be translated into a ‘level of leakage,’ which tells a weatherization expert how much air sealing needs to be done. The harder it is to pull air through the fan the harder it is to pull extra air through exterior cracks or holes, which means the house is at a lower level of leakage.

Why Get a Blower Door Test?

Blower door tests aid weatherization experts in finding individual air leaks by rapidly drawing outside air into a home, which makes a rapid passage of air that can be felt by hand. Once these areas of leakage are identified they can be addressed by adding things like caulking, dry wall, fiberboard, door sweeps, and weather-stripping. As important as air sealing is to home weatherization, it is crucial to remember that a home can be sealed too tightly from outside air negatively affecting indoor air quality (IAQ). There are two important reasons that buildings have some leakage, firstly every house needs to breath in order to maintain a proper level of moisture into and out of the building. And secondly, combustion appliances like gas furnaces also need some leakage to create the small pressure difference that moves combustion gases out of a home through vents. So not only can a blower test tell a homeowner how much insulation or air sealing they need, it can also highlight safety issues if the building is too tight.

How Do I Get a Blower Door Test?

The actual process of conducting a blower door test is not too complicated, but the equipment required and the expertise needed to analyze the data are factors that make it a good idea to get professional help. Many insulation companies provide blower door tests; they often do both pre-and-post insulation tests to assess the quality of their work. Sometimes companies offer the tests as part of a larger energy-audit package that can be useful to a homeowner looking for a variety of ways of reducing their energy consumption. Expect to pay anywhere from $200-400 for such a service.

Further Resources

1. http://www.sheltertech.com/bdt.htm
2. Home Energy Magazine on blower doors
3. Infiltec Weatherization Directory