Blower Door: Friend or Foe?

Originally published by the following source: SBC MagazineOctober 10, 2019
by Jay Crandell, P.E. with contributions from ABTG Staff and Professional Engineers

   

Three previous articles in this series addressed the significance of air leakage control, various air barrier materials and methods, and installation and inspection practices. In this fourth and final article, we address blower door air-leakage testing.

Blower Doors and Code Requirements

At the most basic level, a blower door air-leakage test uses a door with a fan (blower) and instrumentation to monitor air flow and pressurization (or depressurization) of the building at standardized test conditions (see Figure 1). Based on the geometry of the building, the air flow rate is then converted to an ACH value (i.e., air changes per hour for the enclosed, conditioned volume of the building at a specified pressure differential) or CFM/ft2 value (cubic feet of air leakage per minute per square foot of exterior enclosure surface area).

Typically, these tests and the required calculations are performed by a blower door or envelope or energy rating consultant. Additional information on air-barriers, installation, and testing can be found at Resources for Air Barriers.

Blower door tests have become commonplace with the adoption of a requirement for air-leakage tests for one- and two-family dwellings in 2012 and later editions of the IECC residential energy code (see Table 1 and Figure 2). While air-leakage testing remains optional in the IECC commercial energy code provisions (even though the code does include a maximum air leakage target), air-leakage tests are increasingly used on a project-by-project basis to verify and deliver properly performing commercial buildings. Thus, air-leakage testing as required or used as good practice is being driven by a growing appreciation for the significance of air leakage control.

Table 1: 2009 vs. 2012/2015/2018 IECC - Residential

Climate Zone 2009 IECC 2012/2015/2018 IECC
1-2 < 7 ACH ≤ 5 ACH @ 50 pascals
3-8 < 7 ACH @ 50 pascals ≤ 3 ACH @ 50 pascals
Air sealing list & visual inspection Yes Yes
Blower Door Test Not required Required

ACH = air changes per hour; a measure of building air tightness.

Figure 2: U.S. Climate Zones

Figure 3: Example Blower Door Test Report from Consultant

For those concerned with delivering a code-compliant and energy efficient building, the blower door air-leakage test is your friend. The blower-door test complements the application of any type of air barrier material and method. It also complements the effort to follow prescriptive practices for air barrier installation and inspection by helping to detect and correct missed leakage paths. This is typically done by use of tools like “smoke sticks” or even infrared cameras while the building is pressurized or depressurized by the blower door. It provides assurance that the target air leakage rates are met and this will also provide assurance that the building will perform with energy savings, comfort, and moisture-control performance as intended by the code or by design. 

In addition, if HVAC equipment are properly sized, then ensuring that air leakage rates are consistent with the assumed building air-leakage rate is very important to the performance of the HVAC system. Hence, there are many good reasons to perform a blower door test to demonstrate code compliance. 

Example Blower Door Results

Now that we have established what a blower door test is, how it is used, and its many benefits, it is time to put it into practice and look at some results. Figure 3 is an image of an actual blower door test consultant’s report to the builder. The test report indicates an ACH of 2.397 (rounded to 2.4) which is comfortably below the maximum allowed 3 ACH for the subject house in Climate Zone 4 (see Table 1 and Figure 2). 

Figure 4: Example “Energy Efficiency Certificate”

To readily convey this information to the building inspector and the home owner (including future home buyers), the result also is included on a code-required “energy efficiency certificate” placed on the home’s electric panel (Figure 4). This certificate is extremely important to the value of an energy efficient home as the information on this certificate is not easily seen or otherwise known. Clearly, the blower door is a valuable friend of the builder, inspector, and building owners or future buyers.

For more information on air-barriers and air-leakage control, refer to the Air Barrier Topical Library on Continuousinsulation.org.

For additional information, please review the following articles and videos:

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