What is a good CFM for a blower door test is measured as CFM50, cubic feet per minute of air needed to keep house at 50 Pascals pressure, and what is considered good depends on house size. To normalize for size, auditors also calculate ACH50 air changes per hour, which is CFM50 times 60 divided by house volume. For a typical 2000 square foot home with 8 foot ceilings, volume is 16000 cubic feet. A very leaky old home might be 4000 CFM50 which equals 15 ACH50, poor. A moderately leaky home might be 2500 CFM50 which equals about 9 ACH50. A good target for existing homes after weatherization is 1500 CFM50 which equals about 5.6 ACH50. For new construction meeting current International Energy Conservation Code, good is below 1500 CFM50 and often required below 3 to 5 ACH50 depending on climate zone, for example IECC 2021 requires 3 ACH50 in many zones. An excellent very tight home might be 800 to 1000 CFM50 which equals 3 ACH50 or less, and passive house is below 0.6 ACH50, which for this house would be about 160 CFM50. So good is generally under 1500 CFM50 for average house, or under 5 ACH50.
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