Duct Leakage Testing Requirements & Workforce Standards

Duct Leakage Testing Requirements & Workforce Standards

Effective January 1, 2026

The 2025 California Mechanical Code (CMC) establishes statewide requirements for duct leakage testing that improve HVAC system quality, energy efficiency, and accountability. For the first time, California also establishes minimum workforce qualifications for individuals performing duct leakage testing, ensuring that testing is completed by qualified, third-party certified technicians rather than unqualified personnel.

What Does the 2025 CMC Require?

Duct Leakage Testing

Section 603.9.2 requires ductwork to be leak tested in accordance with the SMACNA HVAC Air Duct Leakage Test Manual. The code establishes:

• Standardized leakage testing procedures

• Representative sampling of installed duct systems

• Escalating testing requirements – Test 10% of the installed ductwork initially. If that sample fails, expand testing to 40%. If the 40% sample also fails, 100% of the installed ductwork must be tested until compliance is achieved. 

• Leakage limits based on SMACNA Duct Leakage Class criteria

• Testing at the system design pressure

The CMC also references California Energy Code (Title 24, Part 6) duct leakage testing requirements where applicable for residential, multifamily, and nonresidential buildings.

New Workforce Standards

Perhaps the most significant change is that the 2025 CMC now requires duct leakage testing to be performed by certified technicians.

Acceptable certifications include:

• TABB – Testing, Adjusting and Balancing Bureau

• AABC – Associated Air Balance Council

• NEBB – National Environmental Balancing Bureau

• Other equivalent agencies approved by the Authority Having Jurisdiction (AHJ)

This represents a major advancement from previous code editions by recognizing that accurate duct leakage testing depends not only on following a testing procedure, but also on the qualifications of the individual performing the work.

Why the TABB DALT Technician Makes Sense

Among the recognized certifications, the TABB Duct Air Leakage Testing (DALT) Technician certification is uniquely focused on duct leakage testing.

A DALT Technician is specifically trained to:

• Understand duct leakage standards and code requirements

• Prepare HVAC systems for leakage testing

• Properly conduct duct leakage tests

• Gather and interpret test results

• Complete required documentation and reports

• Perform leakage testing in both new construction and existing buildings

Because the certification is dedicated entirely to duct leakage testing, the DALT credential directly aligns with the technical knowledge and field skills required by Section 603.9.2.

Looking Ahead – 2027 UMC

The 2027 Uniform Mechanical Code (UMC), anticipated to become the 2028 California Mechanical Code, is expected to further clarify this workforce requirement by specifically recognizing that a TABB DALT Technician may perform duct leakage testing.

This clarification recognizes what already exists in practice: the DALT certification is designed specifically for technicians whose primary responsibility is conducting duct leakage testing in accordance with SMACNA procedures and mechanical code requirements.

Benefits to Building Owners

Qualified duct leakage testing helps ensure:

• Reduced energy loss

• Improved HVAC system performance

• Better occupant comfort

• Lower operating costs

• More accurate commissioning and verification

• Consistent statewide testing practices

By combining nationally recognized testing procedures with qualified workforce requirements, the 2025 California Mechanical Code improves both the quality of construction and the reliability of compliance verification.

✔ Effective January 1, 2026

✔ Duct leakage testing must follow the SMACNA HVAC Air Duct Leakage Test Manual

✔ Testing must be performed by technicians certified through TABB, AABC, NEBB, or another AHJ-approved equivalent organization

✔ The TABB DALT Technician certification is specifically designed for duct leakage testing and provides focused expertise in testing procedures, reporting, and code compliance.

✔ The 2027 UMC (future 2028 CMC) is expected to explicitly recognize the TABB DALT Technician as an appropriate credential for performing duct leakage testing, further aligning workforce qualifications with the specialized nature of the work.