How to Estimate Natural Air Infiltration Rates

Written by keith allen
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How to Estimate Natural Air Infiltration Rates
A variable-speed fan is an essential component in measuring natural ventilation. (Fan detail image by TekinT from

Air infiltration, sometimes referred to as natural or passive ventilation, is the measurement of air entering or leaving the house. This occurs naturally due to wind and differences between indoor and outdoor temperatures. Estimating the rate of infiltration helps determine the effectiveness of the insulation and weather stripping of the home.

Skill level:

Things you need

  • Door blower system

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  1. 1

    Close all doors, windows and any other openings that would normally be closed during the winter heating system except for a single door.

  2. 2

    Mount the blower unit, including a temporary covering of the door, on the door. Along with a fan and covering, the unit includes air pressure gauges.

  3. 3

    Operate the fan blowing air out of the home. This lowers the air pressure within the home. Monitor the air pressure gauges included with the door blower unit assembly.

  4. 4

    Consult the charts included with the door blower system to determine the rate of air infiltration. The system compares the differences between the air pressure indoors and outdoors. Testing is performed in various methods and the length of time the blower is operated also plays a part. In the end, an estimate of the of the natural infiltration of the home is determined.

Tips and warnings

  • The blower door system is useful to determine the overall air infiltration of a home but it doesn't isolate the locations of the air leaks. It is commonly performed as a before and after test during weatherization projects. It proves the efficiency, or lack thereof, of the changes made to the home. Computer software provided with the door blower system estimates the size of the openings and the volume of the air leaks.
  • Check pilot lights of gas appliances after the test is run. The low indoor air pressure may extinguish the pilot lights and require them to be restarted after the blower door test is complete.

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