Glossary · Testing & air leaks
CFM50
Also called: CFM@50Pa · CFM50 leakage · cubic feet per minute at 50 Pa · cubic feet per minute at 50 pascals
The raw air-leakage result of a house's fan test: how many cubic feet of air per minute the fan must move to hold the house at test pressure.
What it means
During a blower door test the fan's airflow at 50 pascals (see 50 Pa) is recorded as CFM50. A bigger number means more leakage, but bigger houses naturally leak more, so it's usually converted to ACH50 for comparisons. Comparing CFM50 before and after air sealing shows how much leakage the work removed.
Why it matters in an audit
It's the measurement that ACH50 is calculated from and the number that feeds the energy model behind your audit report.
Typical numbers
Reference values with their sources. Your auditor’s report gives the figure for your own house.
| What | Value | Source |
|---|---|---|
| Converting to ACH50 | ACH50 = CFM50 × 60 ÷ house volume (ft³) | Arithmetic (definition of ACH50) |
| Worked example | A 16,000 ft³ house measuring 800 CFM50 = 3.0 ACH50 | Arithmetic |
| Metric conversion | 1 CFM ≈ 0.472 liters per second (1 m³ = 35.3147 ft³) | natural-resources.canada.ca ↗ |