What Is A Blower Door and Why Is It the Tool of Choice Among Energy Audit Professionals?

A blower door can pinpoint air leakage in a building. Why is this important? Because air leakage causes much of the discomfort that we feel inside a building.The blowers are used by Energy Audit Professionals to help pinpoint pesky airleaks.

I've already mentioned in earlier posts that energy audits are a commen service of mine here in Michigan. During a recent audit, the customer was bothered by cold drafts in the master bath. I turned on the blower door and cold air came rushing in through both ceiling mounted exhaust fans and all of the ceiling mounted recessed light fixtures. I found twelve inches of fiberglass batt insulation in the attic above. Further investigation revealed that both exhaust fans discharged into the attic. The recessed light fixtures were rated for insulation, but not rated at preventing air flow through them. In addition, the openings in the drywall ceiling were not sealed or gasketed. The repair was easy. Merge all bathroom exhaust fans at a single location and run that vent to the exterior. Include a damper at the exit point. Replace the recessed light fixtures with fixtures rated to prevent air movement through them, and provide gaskets at the drywall openings.

What else can a blower door find? The most common location for air leaks is the attic access cover or door. These covers are not weatherstripped and only gravity holds them in place. No wonder air rushes through these during a blower door test.

Another common location is where the basement meets the crawl space. The openings into the crawl space are not properly sealed, and air rushes into the basement. My experience with this condition usually causes me to re-light the water heater pilot light. Entry doors usually have some air flow deficiency at the threshold or the jambs. Casement windows never close completely and air rushes in around the perimeter during a blower door test. Air rushing in through outlets and switches on exterior walls can blow out a candle.

The specific blower I use is a Minneapolis Blower Door Model 3 with a DG-700 digital gauge. Made in Minneapolis (no fooling) by the Energy Conservatory it is the most common blower door in use today(pictured above). It provides me with an air flow across the fan at a given pressure. This actual air flow is compared the Building Performance Institute's (BPI) building airflow standard. The BPI building airflow standard (BAS) is a theoretically "perfect" air flow that eliminates unnecessary air flow while maintaining an acceptable comfort level for the building's occupants. Every building in which I have run a blower door test had an actual air flow greater than the building's BAS of between 25% & 200%. I tell my customers, "Your building has many opportunities for improvement." Some just more than others.