March 25

What is a Blower Door Test?


Blower door testing photo

Blower door testing being completed on a historic log home to find air (and insect) leaks.

A blower door test measures and identifies air leakage in a building using a special door. The door looks like a box fan but has airflow and pressure measuring devices inside it. Running the fan at different settings simulates different conditions and helps identify air leakage rates and locations.

Why do a blower door test?

This diagnostic tool assists in doing an energy audit to

  • verify building code requirements and
  • to help identify and solve issues with windows, doors, and other exterior systems.

Verify building code requirements

Used as a quality assurance tool, a blower door test can determine if all a building’s mechanical, engineering, and plumbing (MEP) systems meet design requirements and building codes.

For example, a typical mechanical system tested is the HVAC system. 

Identify building tightness problems

In a building, air can leak into or out of it in many different places. Building tightness problems cost money & can incur additional issues. For example, imagine trying to heat or cool your house with your windows open. The HVAC system would run more frequently to reach and stay at the temperature set on your thermostat. The result of all this extra energy consumption is high energy bills and excess wear and tear on your HVAC system!

Stopping air leakage by identifying and sealing the leakage issue(s) conserves energy. In addition, it prevents moisture, pollutants, and insects from entering the building. According to, these are some reasons for establishing the proper building tightness:

  • Reducing energy consumption due to air leakage
  • Avoiding moisture condensation problems
  • Avoiding uncomfortable drafts caused by cold air leaking in from the outdoors
  • Determining how much mechanical ventilation might be needed to provide acceptable indoor air quality.

How does blower door testing work?

A blower door test pressurizes a building to simulate different conditions and find air leaks. Here’s how:

First, a building’s exterior door is fitted with a blower door. During testing, the high-powered fan on the blower door blows air into or exhausts air out of the building. The fan’s speed increases or decreases internal building pressure and allows air to move through pathways, such as cracks or openings, finding air leaks in the building. The fan measures how much air is moving in or out of a building. 

Using the resulting pressure measurements and the amount of air moving through the fan into the building allows for calculations to determine the amount of air leaking out of the building or air leakage rate. The air leakage rate is then compared to historical data (e.g., energy bills) to determine its effect on energy consumption.

How do we determine where the building is leaking air? 

BEPG uses additional tools to determine the location of air leaks. Standard methods include infrared thermography (camera able to see surface temperature differences and display it as a picture), smoke pencils/pens, or theatrical fog. These methods each require knowledge of building construction and science to analyze and determine leak sources appropriately.

How big of a building can BEPG test for air leakage? 

BEPG has three (3) fans which can produce approximately 3,500 to 4,000 cfm. The International Energy Conservation Code (IECC) defines Air Changes Per Hour (ACH) allowed at a specified pressure. Depending on the test pressures required to achieve needed building-code air-tightness, BEPG can test up to approximately 200,000 ft3 buildings. We also have access to additional equipment and techniques for more significant buildings if necessary. 

Contact us for specific details on air leakage testing of whole buildings using blower doors.


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