CSLB C-20 HVAC ContractorPlanning and LayoutHard
A newly installed duct system has a total supply and return airflow of 1,200 CFM. Duct leakage testing (CFM25) measures 65 CFM of total leakage. Title 24 requires new duct systems to have total leakage no greater than 6% of total system airflow. Does this system meet the leakage requirement?
- ANo, because any measurable leakage fails Title 24 compliance
- BYes, because 65 CFM of leakage equals about 5.4% of total airflow, which is below the 6% threshold
- CNo, because 65 CFM exceeds the 6% threshold based on total airflow
- DYes, but only because the system is exempt from CFM25 testing at this airflow
Show answer & explanationAnswer & explanation
Correct answer: B. Yes, because 65 CFM of leakage equals about 5.4% of total airflow, which is below the 6% threshold
Percent leakage is calculated as (leakage CFM ÷ total system CFM) × 100 = (65 ÷ 1,200) × 100 ≈ 5.4%. Since 5.4% is less than the 6% maximum allowed for new duct systems under Title 24, the system passes the leakage test.
Why the other options are wrong
- A. Title 24 allows a defined leakage tolerance, not zero leakage.
- C. The math shows 5.4%, which is under, not over, the 6% limit.
- D. No such exemption applies to standard new construction duct systems requiring testing.
Title 24 Duct Leakage (CFM25)
Title 24 requires new residential duct systems to be tested for leakage using a CFM25 test, with total leakage typically limited to 6% of total system airflow.
- Percent leakage = (leakage CFM ÷ total system CFM) × 100
- CFM25 test pressurizes ducts to 25 Pascals to measure leakage
- Excess leakage wastes energy and requires sealing before passing inspection
Memory trick: Divide leakage by total airflow, then check against the 6% ceiling.