I recently attended a BS* and Beer meeting in Kansas City, MO. It took place in a house being built by Jake Bruton’s company, Aarow Building. It is a single-level, slab-on-grade structure, measuring roughly 3250 sq. ft. When I was there, they were just finishing the mechanical, electrical, and plumbing systems and about to move to the insulation phase—an ideal time for a mid-build blower door test.
The purpose of a mid-build blower door test is to confirm the building is on track to meet the desired airtightness metric. In this case, it’s 1 ACH50 or less, which all of Jake’s new homes are contractually bound to achieve. A mid-build test also identifies any missed opportunities for air-sealing.
The simplest blower door test puts the house under negative or positive 50 Pascals (Pa) of pressure and records the cubic feet per minute (CFM) rate of air exchange; this is called a single-point blower door test because it puts the house at just one pressure. If the calculated air changes per hour at 50 Pa (ACH50) number is too high, set the fan on “cruise control” and go find the air leak locations. There’s no need to perform multi-point testing—where CFM rates are measured at progressively lower pressure points, usually starting at 60 Pa—this early in the build. That type of test is most effective and informative when performed toward the end.
This home measured 35,600 cu. ft. and had 9250 sq. ft. of surface area including the floor, walls, and ceiling. The home tested at an impressive 180 cu. ft. per minute of airflow through the fan at the test pressure of -50 Pa (180 CFM50). From this number, we can calculate the air changes per hour and CFM per sq. ft. of surface area metrics:
ACH50 = CFM50 x 60 min.…
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