C-20 — HVAC

A California C-20 Warm-Air Heating, Ventilating and Air-Conditioning contractor license lets you fabricate, install, maintain, service, and repair furnaces, ducted and ductless air-conditioning systems, heat pumps, ventilation systems, and the ductwork and controls that go with them, for hire, on any job where combined labor and materials total $500 or more. (Source: California Business and Professions Code Sections 7028 and 7048.) It’s issued by the CSLB once you pass two separate exams — the C-20 trade exam and the Law & Business exam — and document at least four years of qualifying HVAC experience.

What a C-20 license actually covers

Under California Code of Regulations, Title 16, Section 832.20, a C-20 contractor “fabricates, installs, maintains, services and repairs warm-air heating systems and water heating heat pumps, complete with warm-air appliances; ventilating systems complete with blowers and plenum chambers; air-conditioning systems complete with air-conditioning unit; and the ducts, registers, flues, humidity and thermostatic controls and air filters in connection with any of these systems.” The classification explicitly extends to warm-air heating, ventilating, and air-conditioning systems that use solar energy. In practice, that scope shows up as jobs like:

• Furnace change-outs — removing a failed gas furnace and installing a new high-efficiency unit with a matched plenum and duct transition.
• New-construction duct systems — designing and fabricating a full supply-and-return duct layout, registers, and plenum for a new home, sized to a load calculation.
• Split-system and heat-pump installs — setting the outdoor condenser or heat pump, running refrigerant line sets, tying in the condensate drain, and wiring the thermostat and controls.
• Ductless mini-split installs — mounting indoor heads and an outdoor unit for zoned heating and cooling without central ductwork.
• Commercial rooftop package units — installing or servicing packaged HVAC units on a tenant-improvement job, including economizers, coils, and filter racks.
• Solar-assisted warm-air systems — integrating solar heating components into a warm-air system, which CCR 832.20 specifically folds into C-20’s scope rather than requiring a separate license.

The C-20 exam, section by section

Every CSLB applicant sits two exams: the trade-specific C-20 exam and the Law & Business exam. CSLB allows 3.5 hours per exam, and both are closed-book, multiple-choice with four answer choices, and provide a calculator for questions requiring computation. (Source: CSLB Examination FAQ.) CSLB does not publicly publish the exact number of scored questions or the numeric passing-score threshold for the trade exam, so treat any specific question count or cutoff you see elsewhere as unverified.

What CSLB does publish is the content outline, and for exams scheduled on or after April 1, 2026, the official C-20 study guide breaks the exam into four sections:

• Planning and Estimating — 22% (system design and evaluation, load and psychrometric calculations, duct layout, job cost estimating)
• Fabrication, Installation, and Startup — 38% (duct fabrication, equipment installation, electrical/mechanical/plumbing/refrigeration components tied to HVAC, air distribution, system startup)
• Troubleshooting, Repair, and Maintenance — 20% (diagnostic testing, evaluation, maintenance and repair)
• Safety — 20% (PPE, Cal/OSHA jobsite requirements, handling hazardous materials)

(Source: CSLB License Examination Study Guide, Warm-Air Heating, Ventilating and Air-Conditioning C-20, effective for exams scheduled on or after April 1, 2026.) Fabrication, Installation, and Startup carries the single largest weight on the exam, so hands-on installation sequencing and startup procedure deserve the most study time.

What it takes to qualify

You need at least four years of full-time, journey-level HVAC experience within the 10 years before you apply, at the level of a qualified journeyperson, foreman, supervisor, contractor, or owner-builder — not as an apprentice or unskilled laborer. CSLB will credit qualifying HVAC-related technical education or a registered apprenticeship toward up to three of those four years, but every applicant must still show at least one year of actual hands-on trade experience; classroom time alone can’t substitute for all four years.

On the paperwork and cost side, current CSLB fees are a $450 application/exam processing fee, plus a separate initial license fee of $200 for a sole owner or $350 for any other business type once you pass. (Source: CSLB Application for Original Contractor License; verify current amounts on cslb.ca.gov before you submit, since CSLB fees are set by regulation and can change.) You’ll also need a $25,000 contractor bond, the statewide minimum set by SB 607 since January 1, 2023.

Workers’ compensation deserves special attention for this classification specifically: C-20 is one of only four CSLB classifications — alongside C-8 Concrete, C-22 Asbestos Abatement, and D-49 Tree Service — required to carry active workers’ compensation insurance (or file a certificate of exemption as a qualifying joint venture) since January 1, 2023, regardless of whether you have employees. That’s well ahead of the broader all-classifications workers’ comp mandate, which SB 1455 has since pushed back to January 1, 2028, for every other classification. A lapsed workers’ comp certificate can get a C-20 classification pulled from an otherwise active license, so this isn’t optional paperwork. See our step-by-step application guide and current fee and bond breakdown for the full application sequence.

C-20 vs. the classifications people confuse it with

C-20 vs. C-38 Refrigeration. The dividing line is temperature. C-38 covers refrigeration equipment, refrigerated rooms, and insulated spaces that control air, liquid, or gas temperatures below 50°F (10°C) — think walk-in coolers, freezers, and commercial refrigeration display cases. C-20 covers standard building comfort heating and air-conditioning above that threshold. If the job is a walk-in freezer for a restaurant, that’s C-38; if it’s central air conditioning for the dining room, that’s C-20.

C-20 vs. C-4 Boiler, Hot Water Heating and Steam Fitting. C-4 covers hydronic systems — boilers, hot-water heating, and steam fitting. C-20 covers warm-air (forced-air) systems. A job piping a boiler to steam or hot-water radiators is C-4; a job installing a furnace, air handler, and duct system is C-20. Some larger mechanical contractors hold both, but they’re separate classifications with separate exams.

C-20 vs. C-43 Sheet Metal. C-43 covers sheet-metal fabrication broadly — gutters, flashing, metal roofing, patented chimneys, kitchen equipment, and ductwork fabricated as a standalone product. C-20’s scope already includes the ducts, registers, and plenum chambers that are part of an HVAC system, so a C-20 contractor doesn’t need a separate C-43 to fabricate and install the ductwork for their own HVAC installs. C-43 becomes the right classification when a contractor is only fabricating and installing sheet-metal ductwork on behalf of someone else’s mechanical system, without touching the heating or cooling equipment itself.

Who actually needs this license

C-20 is the license behind most of the HVAC work homeowners and businesses see day to day: residential install and service companies doing furnace and AC change-outs, new-home builders subcontracting mechanical rough-in, commercial tenant-improvement contractors installing rooftop package units, property managers running multi-unit HVAC service contracts, and solar-HVAC integrators pairing solar equipment with a warm-air system. Anyone bidding HVAC work above the $500 labor-and-materials threshold in California needs an active C-20 (or a properly licensed subcontractor holding one) on the job.

C-20 exam questions people actually ask

Does C-20 cover ductwork, or do I need a separate sheet-metal license?
C-20’s scope under CCR 832.20 already includes the ducts, registers, and plenum chambers tied to a warm-air heating, ventilating, or air-conditioning system, so no separate C-43 is needed for ductwork you fabricate and install as part of your own HVAC jobs.

Can a C-20 contractor install commercial walk-in coolers or refrigeration?
No. Equipment and spaces controlling temperatures below 50°F fall under C-38 Refrigeration, a separate classification with its own exam.

Do ductless mini-split systems fall under C-20?
Yes. CCR 832.20’s “air-conditioning systems complete with air-conditioning unit” language covers ductless heat pump and mini-split installs, not just central ducted systems.

Do I need workers’ comp insurance if I don’t have employees?
For C-20 specifically, yes, unless you’re a qualifying no-employee joint venture with an exemption certificate on file. C-20 has been on CSLB’s mandatory workers’-comp list since January 1, 2023, well ahead of the 2028 deadline that applies to most other classifications.

How many years of experience do I need to apply?
Four years of full-time, journey-level HVAC experience within the last 10 years, with up to three of those years potentially covered by qualifying technical education or a registered apprenticeship — but at least one year must be hands-on trade experience.

Is the C-20 trade exam open-book?
No. It’s closed-book, multiple-choice with four answer options per question, and CSLB provides a calculator for questions that require computation.

What’s the passing score on the C-20 exam?
CSLB does not publicly publish an exact passing-score threshold or total question count for the trade exam. Treat any specific number you see elsewhere as unofficial and unverified.

Are solar warm-air heating systems covered under C-20?
Yes. CCR 832.20 explicitly states the classification includes warm-air heating, ventilating, and air-conditioning systems that utilize solar energy.