Definition
Blower Door Test
A diagnostic test that measures a building's air leakage rate by depressurizing the structure with a calibrated fan.
The Full Picture
A blower door test uses a powerful fan mounted in an exterior door frame to pull air out of the building, creating a measured pressure difference (typically 50 Pascals) between inside and outside. The fan's airflow rate at this pressure — measured in CFM50 (cubic feet per minute at 50 Pascals) — indicates how leaky the building is. The result is often converted to ACH50 (air changes per hour at 50 Pascals) for comparison against energy code standards. During the test, energy auditors use smoke pencils or thermal imaging to locate specific air leak locations.
Why It Matters
Why field professionals need to document this
The blower door test is the single most important diagnostic in a home energy audit. It quantifies what 'drafty' actually means in numbers, identifies priority air sealing locations, and verifies the effectiveness of weatherization work. Many utility rebate programs require blower door testing before and after improvements. For energy auditors, documenting the test results alongside thermal imaging findings creates the evidence base for the entire upgrade recommendation.
In a Report
How this shows up in findings
Here's how a blower door test finding looks in a professional field report generated by ReportWalk:
Pre-retrofit: 2,850 CFM50 (8.2 ACH50) — significantly above 5.0 target
Post-retrofit: 1,400 CFM50 (4.0 ACH50) — 51% reduction in air leakage
Major leakage locations: attic hatch, rim joist, recessed lights
Relevant For
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