Title 24 Duct Leakage Testing in California

Key Takeaways

Common Question	Short Answer
Does California require duct testing when I replace my HVAC?	Generally yes. Installing new heating or cooling equipment on existing ducts usually triggers a Title 24 duct leakage test. Test your ducts
What is the Title 24 duct leakage limit for existing homes?	For altered systems, the CEC’s 2022 and 2025 forms list 10% or less total leakage, or 7% or less leakage to outside, or sealing all accessible leaks. Confirm your exact target with your contractor or building department.
What about a brand-new duct system?	When at least 75% of the duct system is new material, the CEC forms list a limit of 5% or less. New construction code
Who verifies the test?	A certified third-party rater. Under the 2025 code, HERS raters are now called ECC-Raters, and the check works much the same way.
What happens if my ducts fail?	The ducts must be sealed and retested, or every accessible leak must be sealed and verified. The permit generally can’t be closed until then. How we repair ducts
Can Aeroseal help me pass Title 24?	Usually. Across 38 Bay Area systems, Aeroseal cut leakage from 400 to 54 CFM25 on average. See the results
Does MaxSeal work with HVAC contractors on Title 24 jobs?	Yes. We seal and test ducts alongside the contractor who installs the equipment. For contractors

1. What Title 24 Is

Title 24, Part 6 is California’s Building Energy Efficiency Standards, written by the California Energy Commission (CEC). It applies to new homes and to many alterations in existing homes, including HVAC work. The 2022 code took effect on January 1, 2023. The 2025 code took effect on January 1, 2026, so permits applied for in 2026 generally fall under the 2025 rules.

For existing homes, the duct leakage numbers on the CEC’s alteration forms are the same in both cycles. The main change is the name of the verification program. Requirements can vary with climate zone and project details, so always confirm with your contractor or local building department.

2. What Triggers Duct Testing

Based on the CEC’s alteration compliance forms, a duct leakage test is generally required when:

Heating or cooling equipment is installed in a ducted system, such as replacing a furnace, AC condenser, coil or heat pump
More than 25 feet of duct is replaced in an existing system
An existing duct system is extended by more than 25 feet
An entirely new or replacement duct system is installed

Smaller duct jobs, under 25 feet added or replaced, are listed as exempt from verification. If your project is close to that line, ask your building department.

3. Leakage Targets for Existing Homes

Type of project	Leakage target on CEC forms (2022 and 2025)
Equipment replaced on existing ducts	10% or less total leakage, or 7% or less to outside, or seal all accessible leaks
Existing ducts extended over 25 feet	10% or less total leakage, or 7% or less to outside, or seal all accessible leaks
More than 25 feet of duct replaced	Same as altered systems above
Entirely new or replacement duct system (at least 75% new material)	5% or less total leakage

The percentage is leakage divided by the system’s nominal air handler airflow. For cooling, the forms use 400 CFM (cubic feet per minute) per nominal ton. A 3-ton system works out to 1,200 CFM, so a 10% target is 120 CFM of leakage.

4. HERS and ECC Verification

The installing contractor runs the duct test and records the result. A certified third-party rater then verifies it and registers the paperwork with a data registry. Under the 2022 code this was called HERS verification. Under the 2025 code, the CEC moved field verification into its Energy Code Compliance (ECC) Program, and HERS raters are now recognized as ECC-Raters.

For you, the process looks about the same. Your building inspector will typically want to see the registered verification before finaling the permit. Duct systems already registered as previously sealed and tested may be exempt, as are duct systems built, insulated or sealed with asbestos.

5. What Happens If Your Ducts Fail

After a failed test, the usual next step is finding and sealing the leaks. New ducts are rarely the only answer. Your options usually look like this:

Seal and retest. Repair large gaps by hand and seal the rest, then test again to meet the percentage target.
Seal all accessible leaks. If the target can’t be reached, the code allows sealing every accessible leak instead, with the rater verifying the work.
Replace sections. Badly damaged runs may need replacement, which can change which target applies.

Hand sealing alone often struggles to reach hidden leaks inside walls and floors. That’s where sealing from the inside helps.

6. How Sealing Helps You Pass

Aeroseal seals ducts from the inside. It blows sealant through the pressurized system so it builds up at leaks up to about 5/8 inch, including leaks you can’t reach. A computer tracks the leakage dropping in real time.

In MaxSeal’s 38-system data, average leakage fell from 400 to 54 CFM25, an 86% reduction. 18 of 35 systems with a final reading finished at 50 CFM25 or less. On the 3-ton example above, 50 CFM would be about 4%, well under a 10% target. Results vary, and your rater’s test conditions govern.

Our Typical Title 24 Duct Sealing Process

Baseline test. We measure total leakage at 25 Pa and airflow at every register.
Hand repair. We fix disconnections and gaps too large for Aeroseal.
Aeroseal sealing. We isolate the furnace and coil, block the registers and seal with live monitoring.
Final test. We retest and give you a before-and-after report.
Hand off. Your HVAC contractor and rater complete the code paperwork and verification.

7. Timing Your Duct Work

The best time to test is before the new equipment goes in. If the ducts are leaky, sealing can be scheduled on the same day or the day before the changeout, so the verification test passes the first time. Sealing usually takes one day per system.

If your equipment has already been replaced and failed verification, sealing afterward works too. Your contractor’s rater simply retests. Build a few extra days into your schedule for sealing and retesting, especially during peak summer and winter seasons. For homes being built from scratch, see meeting code in a new construction home.

8. Working With Your HVAC Contractor

MaxSeal doesn’t install furnaces, air conditioners or heat pumps. We focus on ducts. Many HVAC contractors bring us in when a home’s ducts are too leaky to pass by hand sealing alone. You can also hire us directly and share our report with your installer.

Before your project starts, it helps to settle a few things with your contractor. Ask who pulls the permit, who arranges the rater, and who pays for sealing if the ducts fail. Ask whether they plan to test the existing ducts before the changeout or only after. Our before-and-after report gives everyone the same numbers to work from. See our page for contractors.

Conclusion

When you replace HVAC equipment in an existing California home, Title 24 usually requires a duct leakage test verified by a third-party rater. The CEC’s forms list 10% total leakage, 7% to outside or sealing all accessible leaks for altered systems, and 5% for entirely new duct systems.

Testing before the changeout tells you where you stand. If your ducts are leaky, sealing usually brings them well under the target and improves comfort at the same time.

Get a Free Consultation or call (408) 400-3630.