Why should I consider this test?
Air leakage is invisible, difficult to attribute to any single trade, and almost impossible to assess accurately without measurement. A building can have a fully specified and inspected air barrier system and still leak far more air than intended — because air infiltration is the cumulative result of hundreds of small decisions made by multiple trades across the entire construction sequence. ASTM E779 blower door testing converts that complexity into a single, objective number. It does not matter how many inspections were performed or how many submittals were approved — the fan pressurization test measures what was actually built, not what was specified.
As commercial energy codes have tightened, the stakes around that number have risen. ASHRAE 90.1-2019 and later editions include mandatory air leakage limits for commercial buildings that must be verified by testing — not by documentation review. In Vermont and the Northeast, where heating loads dominate and the energy cost of air infiltration is substantial, the difference between a building that tests at 0.20 cfm75/ft² and one that tests at 0.45 cfm75/ft² represents a meaningful, lasting difference in operating cost and occupant comfort. When a building falls short of its target, E779 data also supports efficient remediation — by isolating zones and temporarily sealing suspect areas, the team can narrow down where leakage is concentrated before deploying diagnostic tools like ASTM E1186 to find specific deficiencies.
