A blower door pressurizes the home with a calibrated fan and measures how much air leaks at 50 Pascal pressure (ACH50). Pre-foam baselines for Cincinnati homes typically run 7-12 ACH50; well-foamed homes drop to 3-5 ACH50. The test quantifies what the foam actually achieved.
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A blower door is a calibrated fan that mounts in an exterior door frame and either pressurizes or depressurizes the home to 50 Pascals (about 0.2 inches of water column, equivalent to a 20 mph wind on all sides simultaneously). The test measures the air-flow rate required to maintain that pressure differential; that flow is the air leakage rate. The standard residential unit is ACH50 (air changes per hour at 50 Pascals), which normalizes the flow rate against the home's volume. Typical Cincinnati pre-foam baselines: 7-12 ACH50 for pre-1980 homes, 5-8 ACH50 for 1980-2000 homes, 3-6 ACH50 for post-2000 code-compliant new construction. Typical post-foam results on retrofit projects: 3-6 ACH50, a 40-60 percent reduction. New construction with whole-home foam can hit 1.5-2.5 ACH50, well below current Cincinnati code minimum (the 2021 IECC requires 3.0 ACH50 maximum for new construction in Climate Zone 4). What the test reveals beyond the headline number. (1) Pressure-pan tests at individual ducts and registers identify duct leakage to outside the conditioned space, often a bigger energy loss than envelope air leakage. (2) Thermal imaging during the blower-door pressurization shows exactly where the remaining air leaks are; this guides the foam-install scope decision (rim joist vs attic vs walls priority). (3) Combustion safety testing during depressurization checks that gas appliances (furnace, water heater, range) do not backdraft under negative-pressure conditions. Cincinnati BPI-credentialed installers run a pre-install blower door for diagnostic purposes and a post-install blower door for verification. The two readings give the homeowner a defensible quantification of what the foam achieved. Homeowners should request both readings in the closeout package. A foam install without blower-door verification is a foam install without a measurement of what the homeowner actually bought.