Purpose of Blower Door Tests
Energy Auditors perform blower door tests 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 tests are one indicator of your home’s energy efficiency. You may be able to schedule an energy audit that includes a blower door test. Look for 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.
Blower door tests measure airflow through the blower door in cubic feet per minute at 50 pascals of pressure. A pascal is a very small unit of air pressure. To maintain the 50 pascals of pressure difference, 1 cubic foot of air must enter the house for every cubic foot of air leaving the house through the blower door. That incoming cubic foot of air comes through air leaks. This air leakage rate is measured in cubic feet per minute at 50 pascals or CFM50.
Generally, you can compare the CFM50 from the blower door tests 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. However, the need for ventilation increases as air leakage is reduced.
Reasons to Test
Although air leakage does dilute pollutants and provides 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-electric 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.