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California Title 24 Duct Tightness Test SOP

SOP Compliance Updated Jun 19, 2026 ยท HVAC

Why this matters

California Title 24, Part 6 (2022 Energy Code, effective 1/1/2023) requires duct leakage verification on most altered or new forced-air systems in single-family and small multifamily buildings. The work is verified by a HERS Rater registered with a CEC-approved provider. If the test is not registered to the CF2R/CF3R chain, the city will not green-tag the permit, the contractor cannot close the job, and progress billing stalls. The leakage thresholds and the duct-sealing exceptions are not optional and not negotiable at inspection.

When the test is required

Per Title 24, Part 6, Section 150.2(b)1Ei (residential alterations) and Section 150.0(m) (new construction), a duct leakage test is required when any of the following occur in climate zones 2 and 8 through 16:

  • New forced-air system installation (furnace, heat pump air handler, or packaged unit)
  • Furnace or air handler replacement in an existing duct system
  • More than 40 linear feet of accessible duct replaced or extended
  • Cooling coil or evaporator replacement when the existing duct system has not been previously tested and registered

Climate zones 1, 3, 4, 5, 6, and 7 follow the same trigger list but with different leakage thresholds (see next section). Verify the climate zone using the CEC climate zone map; do not assume by county since several California counties span two zones.

Leakage thresholds and pass criteria

The 2022 Title 24 Energy Standards (Reference Residential Appendix RA3.1.4.3) set the following ceiling for total leakage at 25 Pa:

  • New construction, entirely new duct system: 5 percent of nominal system airflow, or 25 CFM, whichever is greater
  • Existing duct system with furnace or air handler change-out only: 15 percent of nominal system airflow
  • Smoke test alternative (RA3.1.4.3.9): allowed for existing systems where the rater documents that the duct system has no leaks visible to the smoke

Nominal airflow is 400 CFM per ton of nominal cooling capacity, or as specified on the equipment nameplate AHRI rating. A 3-ton system targets 1,200 CFM; the 15 percent threshold is 180 CFM at 25 Pa.

Step by step test procedure

  1. Confirm the air handler, furnace, registers, and grilles are installed and accessible. The system must be substantially complete; you cannot pre-test before grille installation.
  2. Tape or seal all registers and grilles using mastic-coated cardboard or the manufacturer's seal plates. Painter's tape alone will leak; use foil HVAC tape rated to UL 181B-FX.
  3. Connect the duct blaster fan to the air handler cabinet through the return-side service panel or the largest return grille. Disconnect the air handler blower or de-energize the unit so the blaster fan is the only air mover.
  4. Run the duct blaster to pressurize the duct system to 25 Pa positive relative to the conditioned space.
  5. Record the measured airflow at 25 Pa from the calibrated fan flow ring. This is total leakage CFM25.
  6. Compare CFM25 to the applicable threshold from the prior section.
  7. If the system fails, seal accessible joints with UL 181A-M or 181B-FX rated mastic, re-test, repeat until pass.
  8. The HERS Rater registers the CF2R-MCH-20-H (test data) and CF3R-MCH-20-H (verification) to the CEC-approved HERS Provider data registry. The contractor cannot self-register; this is the rater's certification.

Common reasons for failure

  • Plenum-to-air-handler joint sealed with cloth duct tape (UL 181 prohibits)
  • Flex duct inner liner not pulled fully over the collar; outer jacket sealed but inner liner leaking
  • Disconnected boots above the ceiling that the rough-in inspector missed
  • Return-air drop using building cavity as a duct (prohibited under Section 150.0(m)11)
  • Air handler cabinet panel screws missing or gasket compressed past service life

Documentation chain

The compliance documentation chain for a Title 24 duct alteration:

  • CF1R-MCH-04-H: Contractor's installation certificate, signed by the responsible person
  • CF2R-MCH-20-H: HERS Rater's measured leakage data, registered to a CEC-approved provider
  • CF3R-MCH-20-H: HERS Rater's verification certificate, registered to a CEC-approved provider

All three must be in the registry before the building department will issue final approval. Confirm rater registration at the California Energy Commission Approved HERS Provider list before scheduling.

Do not test with the air handler blower running. The blaster fan output is calibrated only when it is the sole air mover. Running both produces an invalid CFM25 reading and a failed registry submission that voids the rater's certification on that job.

References

  • California Code of Regulations, Title 24, Part 6, Sections 150.0(m) and 150.2(b)1Ei (2022 Energy Code)
  • California Energy Commission Reference Residential Appendix RA3.1.4.3 (Duct Leakage Diagnostic Test)
  • UL 181A and UL 181B Standards for Closure Systems for Use with Rigid and Flexible Air Ducts
  • ANSI/ASHRAE Standard 152-2014 Method of Test for Determining the Design and Seasonal Efficiencies of Residential Thermal Distribution Systems

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