Duct Leakage Testing: What It Is and Why It Matters
What Is Duct Leakage Testing?
Duct leakage testing is a diagnostic procedure that measures how much conditioned air escapes from your HVAC ductwork before reaching the living space. In California, duct leakage testing is one of the most frequently required HERS verification measures under Title 24.
How Is Duct Leakage Measured?
A HERS rater uses a calibrated fan and pressure gauge called a duct blaster to pressurize the duct system to 25 Pascals. The fan speed required to maintain that pressure indicates the leakage rate, measured in cubic feet per minute (CFM25). This value is then compared against the maximum allowed by the CF1R energy compliance report.
What Are the Leakage Limits?
For new construction in California, total duct leakage must typically not exceed 4 percent of the nominal system airflow. For HVAC replacements and alterations, the requirement may be 8 percent or 15 percent depending on the scope of work and accessibility of the duct system.
Tips for Passing Duct Leakage Testing
Seal all duct joints with mastic or approved tape before the test. Pay special attention to connections at the air handler, register boots, and takeoffs. Flex duct connections should be secured with zip ties and sealed with mastic. Schedule the test before drywall is installed so any leaks can be easily located and repaired.