California C-20 license exam prep

Reference codes you'll be tested on

The CSLB C-20 trade exam is closed-book, but the questions are pulled directly from the same code books California requires on the job. The CSLB's published C-20 Study Guide names these reference categories:

• California Mechanical Code (CMC) — Title 24, Part 4. Pre-printed by IAPMO with California amendments to the Uniform Mechanical Code.
• California Building Code (CBC) — Title 24, Part 2 — penetrations, fire dampers, structural support of equipment.
• California Plumbing Code (CPC) — Title 24, Part 5 — condensate, gas piping, water heater venting.
• California Electrical Code (CEC) — Title 24, Part 3 — disconnects and branch circuits for HVAC equipment.
• California Energy Code — Title 24, Part 6 — duct sealing, refrigerant charge, HERS verification.
• Business and Professions Code, Division 3, Chapter 9 — the Contractors' State License Law tested on the Law and Business exam.

The 2025 edition of Title 24 was published July 1, 2025, with a statewide effective date of January 1, 2026. As of today, the 2025 California Mechanical Code is the current edition in effect — confirm at the California Building Standards Commission.

Five California-specific rules that trip people up

1. Title 24 Part 6 owns the energy story. California layers a stringent Energy Code on top of the mechanical code. Duct leakage testing, refrigerant charge verification, and HERS rater sign-off are common on alterations and replacements — and on the exam. Don't assume an installation that meets the IMC also meets Title 24 Part 6.
2. CARB regulates refrigerants separately. The California Air Resources Board's Refrigerant Management Program requires registration, leak inspections, and recordkeeping for many commercial refrigeration and large stationary HVAC systems. Federal EPA Section 608 is the floor — California is the ceiling.
3. Seismic anchorage is on every rooftop unit. California amends the CBC and CMC for seismic restraint of mechanical equipment. Rooftop units, suspended equipment, and gas piping require engineered anchorage. Exam questions key on when restraints, snubbers, and seismic gas shutoff valves are mandatory.
4. C-20 scope has hard edges. C-20 covers warm-air heating, ventilating, and air-conditioning. Hydronic heating belongs to C-36 Plumbing, commercial refrigeration to C-38, and solar thermal to C-46. Pulling a job outside scope is a common Law-and-Business question and a real-world enforcement target.
5. $15,000+ jobs require a license; $500+ requires a written contract. Under Business and Professions Code §7028, performing or bidding work valued at $500 or more in combined labor and materials without a license is unlawful, and home-improvement contracts of $500+ must be in writing under §7159. Both thresholds show up on the Law and Business exam.

Statutory references: California Business and Professions Code, Division 3, Chapter 9 (§§7000–7191); California Code of Regulations, Title 24, Parts 2–6.

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