How you interpret results of a blower door test involves reading key metrics and translating them into actionable insights about your home. The main number is CFM50, cubic feet per minute at 50 Pascals, for example if test shows 2200 CFM50 it means 2200 cubic feet per minute leaks when house is pressurized to 50 Pa, which simulates 20 mph wind on all sides. To normalize for house size, look at ACH50, air changes per hour at 50 Pascals, calculated as CFM50 times 60 divided by house volume, a 2000 square foot home with 16,000 cubic feet at 2200 CFM50 equals 8.25 ACH50, which is moderately leaky. For context, older homes often test 10 to 20 ACH50, Energy Star new homes target 3 to 4 ACH50, and passive house is 0.6 ACH50. Also interpret estimated natural air changes ACHn as ACH50 divided by 20, so 8.25 ACH50 equals about 0.41 ACH natural, meaning about 40 percent of air leaks out per hour under normal conditions. Read report for leak locations found with thermal imaging and recommendations. If below 3 ACH50, you need mechanical ventilation for indoor air quality. Use results to prioritize air sealing work that saves energy and improves comfort.
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