Calculate building airtightness from CFM50 and volume, estimate ACHnat, normalize leakage by envelope area, and check a result against an IECC-style ACH50 limit.
Use measured blower door CFM50 and either direct building volume or floor area times ceiling height.
Runs golden cases against the pure ACH50 calculation functions.
Self-tests not run yet.
Energy raters, builders, auditors, and code officials use an ACH50 blower door calculator to convert measured CFM50 into air changes per hour at 50 pascals. Enter building volume and blower door flow to check airtightness targets, compare code thresholds, and document test results. It makes leakage numbers easier to understand across houses of different sizes.
ACH50 means air changes per hour at a 50-pascal pressure difference. It normalizes blower door leakage by building volume so homes of different sizes can be compared.
Multiply CFM50 by 60, then divide by the conditioned volume of the building. The result is air changes per hour at the test pressure.
Only approximately. Natural air leakage depends on weather, height, shielding, leakage location, and occupant behavior, so ACHnat estimates should not replace measured or modeled ventilation analysis.
Use the conditioned volume inside the air barrier, following the test standard or program rules. Including garages, vented attics, or exterior spaces can distort the ACH50 result.
Requirements vary by jurisdiction, code edition, building type, and climate zone. Always compare results with the locally adopted energy code or program specification.