Think about how much energy it would take to heat your home if you left the front door wide open. Similar to this, leaky homes require more energy to heat and cool, since hot air (generated by a furnace) and cold air (generated by an air conditioner) escape more quickly through the leaks. In turn, this causes your heating and cooling equipment to work double-time and consequently, your monthly utility bill to rise.
The good news is, you can identify how much your house is leaking by performing a Blower Door Test. A Blower Door Test measures the rate of air leakage in a home using a Blower Door. The Environmental Protection Agency describes a Blower Door as a “variable speed fan, mounted in a door frame, used to pressurize and depressurize a house to measure air leakage.” Essentially, picture a large fan that sits within a flexible panel that can be manipulated to fit any normal sized door frame.
To perform the test, set the Blower Door up in an exterior door that opens to the outside and place the fan so that it blows air from inside to out. Once the Blower Door is powered on, the fan will suck air from inside the house and blow it outside at a high rate, essentially depressurizing the home. The rate at which the air is sucked out of the house tells you how leaky your home is, since all air that is going out is being replaced by air entering through leaks in other parts of the house. In essence, the Blower Door Test mimics the air leakage that normally occurs in the home but in the reverse direction and in an exaggerated manner.
A Blower Door measures the rate of air flow in cubic feet per minute (cfm) by a manometer or pressure gauge that it is connected. The higher the cfm reading, the greater the air leakage. According to the Vermont Energy Investment Corporation, “tight houses tend to measure less than 1,200 cfm and moderately leaky homes measure between 1,500 and 2,500 cfm. Homes that measure over 3,000 cfm are considered leaky.”
Beyond just measuring the air tightness of a home, a Blower Door Test can help detect where those leaks are located. While the home is depressurized, you can walk from room to room and identify air leaks with your hand by noticing where there is a strong air current. Smaller, subtler leaks can also be identified using a pencil smoke, a device that emits small puffs of smoke so you can visually identify where the air flow is strongest.
To ensure accurate results, the Department of Energy has outlined a few essential steps you must take before performing the Blower Door Test. First, all windows and exterior doors must be closed. If windows are left open, the rate of air leakage will appear to be much greater than it actually is, since air will be sucked into the house through those open windows to replace the air that the Blower Door is pushing out of the home. Second, open all interior doors. Since a closed door will permit less airflow within the house, leaving the interior doors open will give you truer results. Third, for your safety, turn off all heating equipment and non-electric water heaters and close all fireplace flues and doors. Fourth, cover the ashes in wood stoves or fireplaces with damp newspapers or in a manner that ensures they won’t be blown around during the test. Finally, shut all fireplace dampers, fireplace doors and wood stove air intakes.
Blower Doors are not inexpensive; in fact, they typically sell for $2,500 – $3,200. Since a home really only requires a Blower Door Test once, instead of buying a Blower Door and conducting the test themselves, most homeowners hire an Energy Auditor who will perform the Blower Door Test as a part of a more comprehensive energy audit. Energy audits cost only $200 on average, which buys you a whole-house energy assessment by a trained professional. A Blower Door Test is one of the first steps an Auditor will use to determine the extent of a home’s leakiness.
Blower Door Tests are suitable for new and existing homes. Old homes that require retrofits will likely be more leaky than new homes. Nonetheless, in new homes, a Blower Door Test can determine if the home has been insulated and sealed properly.
For a full demonstration of how a Blower Door Test works, check out this video created by the Green Building Advisor.
Image from Wikipedia, German verion, Differenzdruck-Messverfahren. English: Blower-Door-Test.