Blower door test reveals leaks and drafts

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Cindy Parker

If you have done any research about “tightening up” your home to help reduce costs for heating and cooling, you have probably come across the recommendation to have a blower door test conducted.

This could leave you wondering, “Where is my blower door – and how do I test it?”

The blower door is actually a piece of equipment used by an auditor and is attached to your house during the time of the test. Equipment set up usually takes only about 30 minutes, and the whole test is completed in an hour or two.

A blower door test is performed to help determine the air leakage in your building “envelope.” Air leakage (also called infiltration or exfiltration) is that flow you try to seal out when you are weatherizing your home. Caulk, insulation and weather stripping are all measures to help eliminate air leaks.

During a blower door test, all of your windows and exterior doors are closed; all interior doors (bedroom, bathroom, etc.) are opened. An airtight seal (the door) is fitted into one exterior doorway that is left open. This airtight seal is attached to a portable, high pressure fan (the blower). Pressure gauges are set up to measure the atmospheric pressure inside the house for comparison to outside. The variable speed fan is turned on, with the air blowing out of the house. This should create a negative pressure (suction) on the whole house. If there are many air gaps or leaks in the house, there will be a lot of fresh, outside air pulled in through the leaks because of the suction pressure from the blower. Smoke “guns” or streamers may also be used to help point out the very drafty areas that require sealing.

Depending on the equipment used, you may be provided with information about the total amount of leakage – or you may just have information on the fact that you have leaks and where the primary ones are located. Of course, the more sophisticated the test, the more you will be able to quantify your savings by sealing the leaks. You may get details in terms of air changes per hour (ACH) or in terms of cubic feet per minute (cfm).

Many government and utility companies that are sponsoring weatherization rebate programs use blower door tests to prove the effectiveness of the projects. An initial test is conducted before caulking and sealing gaps. After the leaks are eliminated, another test is performed to provide comparison information. If the results are not a good as anticipated, more air sealing or insulation measures may be implemented to reach the program goals.

The bottom line is, sealing air gaps is a measurable objective; not by just watching for reduced utility bills, but by achieving validation through genuine test methods.