ADU Duct Leakage Testing: When Is It Required?
Only a ducted ADU is tested; a ductless heat pump has no duct test. In a new ducted ADU the ducts may leak no more than 5 percent of air handler airflow at 25 Pa, while additions and alterations get limits from 4 to 10 percent depending on how much duct is new.
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Start with the ducts, not the unit size
If the ADU has no ducts, the compliance manual says duct leakage verification is not required, and the Energy Commission ADU FAQ lists it for ducted systems only.
Find the row that matches
- New detached ADU, or an addition with a new ducted system: 5 percent total leakage at final. A rough-in test allows 5 percent with the air handler installed and 4 percent without it, plus a check after drywall that the boots are sealed.
- Existing ducts extended into an addition, any length: 10 percent total or 7 percent to outside. If neither can be met, seal every accessible leak and pass the ECC-Rater's visual check and smoke test.
- Converted room, altered ducts: more than 25 feet of new or replacement duct triggers the test (5 percent for a whole new duct system, 10 or 7 for an extension), as does a replaced air handler, outdoor unit or coil, unless the system is under 40 linear feet or was already sealed and tested.
- Altered ducts, handlers, coils or plenums in a garage: 6 percent, or the smoke test, at any length.
Turn the percentage into cubic feet per minute
The limit is a share of air handler airflow, measured with the ducts pressurized to 25 Pa. Airflow is taken as 400 cfm per ton for a single indoor unit, 350 per ton of each indoor unit on a multi-split, or 0.5 cfm per square foot of floor when the test precedes the equipment. A 1.5-ton unit gives 600 cfm, so 5 percent is 30 cfm. A 600 square foot ADU tested before its air handler arrives uses 300 cfm, so 4 percent is 12 cfm.
Failure and paperwork
A new duct system has no smoke-test fallback; only altered ducts may use the accessible-leak route. Boots and plenums must be sealed before the visit. The installer completes CF2R-MCH-20-H and the rater CF3R-MCH-20-H. Retests follow the failed test page.
See also residential duct leakage, ducted versus ductless and alteration versus addition. Order from the ADU page.
Common Title 24 Questions
- Do ADUs need Title 24 in California?
- What plans are needed for an ADU Title 24 report?
- How much does an ADU Title 24 report cost?
- How long does an ADU Title 24 report take?
- Does a garage conversion ADU need Title 24?
- Does a JADU need a Title 24 report?
Frequently Asked Questions
No. With no ducts there is no duct leakage verification, though refrigerant charge and other checks can still apply.
A central-return furnace cannot: the Mechanical Code does not allow return air from an existing forced-air system to be discharged into another dwelling unit. Where an extension is allowed it meets the 10 or 7 percent limit or the smoke-test route.
Explore ADU and JADU
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- ADU Heat Pump Requirements in California for 2026 Permits
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- Does an ADU Need HERS Registration?
- ADU Kitchen Range Hood ECC Verification
View all ADU and JADU guides → · Permits and Compliance · Title 24 guide