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On a new ICF home, what should the air changes per hour be on a blower test?

John Porter | Posted in GBA Pro Help on


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  1. Riversong | | #1

    The IRC requires ≤ 7 ACH50.
    Energy Star requires ≤ 5 ACH50 (natural ACH less than 0.5)

    On any new home, I would aim for less then 3 ACH50, but the test is invalid unless performed when the house is complete.

    Energy Efficient Building Association criteria is less than 0.25 cfm of leakage per square foot of building surface area (including floor) @ 50 Pa.

  2. David Meiland | | #2

    Another reference point: the Washington State Energy Code standard starting Jan. 1 establishes a "specific leakage area" standard of .0003 or better (smaller number). To calculate, multiply CFM50 by .055. Divide the result by the product of "conditioned floor area" x 144.

    To meet this standard, an 1800SF house would have to test at ~1413 CFM50. Assuming 8 foot ceilings, the house would have 14,400 cubic feet, and an ACH50 of 5.9. If there are cathedral ceilings, the ACH50 would be lower. My guess is that the code writers figure most houses have some cathedral ceilings, and they're trying to get things to average around 5 ACH50 to match Energy Star.

    That's not a tough standard to meet. I tested a 1960s ranch yesterday... 1400 square feet, 1190 CFM50, the WSEC SLA for that is .00032, almost qualifying. I can get it well above qualifying with a couple of simple air-sealing tasks.

    The EEBA standard Robert mentions above is a bit tougher. A simple 30x60 rectangle with 8 foot ceilings and a crawl space would have 5040 square feet of surface area and be allowed 1260 CFM50.

  3. Bill Bradbury | | #3

    I am a BPI certified Building Analyst, we use a Minimum Building Airflow standard to ensure the proper balance of tight building and fresh air. This varies according to wind exposure and climate zone which is represented by the variable N(18 for a single story home with average wind exposure here in Northern Utah). Minimum CFM @ -50 pa = .35 x volume x N/60. If you are using a fresh air intake system(HRV etc.), then I would shoot for <1 62-89.

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