How do I calculate Air Changes per Hour (ACH)?

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ByBill Graber

The formula is (CFM50 X 60) ÷ the volume of the house.

So if your blower door CFM50 reading is 1000 CFM and house is 30’ x 40’ x 8’ tall, the ACH = (1000 x 60) ÷ (30 x 40 x 8) = 6.25 ACH

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