The Future, Energy Efficiency

Blower door testing

The easiest way to measure building air tightness is with a diagnostic tool called a Blower Door. The Blower Door consists of a powerful, calibrated fan that is temporarily sealed into an exterior doorway. The fan blows air out of the house to create a slight pressure difference between inside and outside. This pressure difference forces air through all holes and penetrations in the building envelope. Blower Door tests are typically performed at a pressure difference of 50 Pa (0.2 inches of water column).

By simultaneously measuring the air flow through the fan and its effect on the air pressure in the building, the Blower Door system measures the air tightness of the entire building envelope. The tighter the building (e.g. fewer holes), the less air you need from the Blower Door fan to create a change in building pressure.

Blower Door

Air tightness measurements are presented in a number of different formats including:

  • air flow (house leakage) at 50 Pa of pressure difference (CFM50)
  • air changes per hour at 50 Pa of pressure difference (ACH50)
  • square inches of leakage area

In addition to assessing the overall air tightness level of the building envelope, the Blower Door can be used to estimate the amount of leakage between the conditioned space of the building and attached structural components such as garages, attics and crawlspaces. And because the Blower Door forces air through all holes and penetrations, these problem spots are easier to find using chemical smoke, an infrared camera or simply feeling with your hand.

Finally, Blower Door measurements can be used to measure the infiltration rate of houses. While the Blower Door doesn't measure infiltration rates directly, test results can be used along with mathematical models to determine the infiltration rates for the purposes of evaluating indoor air quality, the need for mechanical ventilation, and to help with proper sizing of heating and cooling equipment.