What is a Blower Door Test?

A blower door is a tool that an energy auditor uses to measure the air leakage into and out of your home. The blower door blows air out of the house bringing it to a standard pressure. The auditor then measures the air flowing through the blower door which determines the severity of your home’s air leaks. Blower door testing is one indicator of your home’s energy efficiency. You may be able to schedule an energy audit that includes a blower door test with a home performance contractor, a private energy auditor, or a low-income weatherization agency. Energy audits are often part of utility-sponsored energy-conservation programs.

The airflow through the blower door is measured in cubic feet per minute at 50 pascals of pressure (a pascal is a small unit of air pressure). For every cubic foot of air passing through the blower door, another cubic foot of air must enter the house through air leaks to maintain the 50 pascals of pressure. This leakage rate is measured in cubic feet per minute at 50 pascals or CFM50.

Generally you can compare the CFM50 from the blower door test with your square footage of your home’s conditioned floor area. If the CFM50 number is considerably larger than your floor area, your house is excessively leaky and sealing air leaks will make the home more comfortable and energy-efficient. If the CFM50 number is considerably smaller than your floor area, your house is too air-tight and indoor air quality may suffer since you can’t depend on air leakage for ventilation. In this case your house probably needs whole-house mechanical ventilation. If the CFM50 number is within 10% of your floor area in square feet, the air leakage isn’t too severe and the ventilation provided by air leakage is marginally adequate, but energy is also being lost as conditioned air leaves the building. The higher the air leakage the more money and effort you can spend cost-effectively to seal the leaks but as air leakage is reduced the need for ventilation increases.

Although air leakage does dilute pollutants and provide fresh air, it’s not very reliable at these tasks. Air leakage tends to over-ventilate a home during cold windy weather and under-ventilate it during mild calm weather. Occupants in more airtight homes must open windows, use kitchen and bathroom vent fans, and install whole-house ventilation systems as needed to ensure fresh, breathable air. Experts agree that it is far more economical and comfortable to build an airtight home and install a whole-house ventilation system than to rely on air leakage for ventilation.

If your home is drafty and excessively dry during cold weather, leading to static-electricity shocks, then excessive air leakage is probably the cause. If your home is moist with condensation collecting on windows and cooking odors lingering, then your home may be relatively airtight already. Ultimately an energy auditor, through the use of a blower door, can evaluate your home’s airtightness and help decide whether or not air leakage is a serious energy problem.