9.1 Title 24 Part 6 Energy Code Requirements for HVAC Systems

What Is Title 24, Part 6?

Title 24 is the section of the California Code of Regulations that holds the state's building standards, commonly called the California Building Standards Code. It is organized into 12 parts, covering everything from structural design (Part 2, the California Building Code) to plumbing (Part 5, the California Plumbing Code) to mechanical systems (Part 4, the California Mechanical Code, covered in Section 9.3). Part 6, formally the California Building Energy Efficiency Standards (commonly called the "Energy Code"), governs how much energy new buildings, additions, and alterations are allowed to consume for space conditioning, water heating, and lighting.

The California Energy Commission (CEC) -- not the CSLB -- writes and adopts Part 6. The CEC updates the Energy Code on a roughly three-year ("triennial") cycle. The most recent update, the 2025 Energy Code, took effect for building permit applications submitted on or after January 1, 2026, replacing the 2022 cycle. This means the 2025 cycle is the version currently governing new C-20 work. As a practical rule, it is the date the building permit application is submitted -- not the construction start date or completion date -- that determines which code cycle applies to a given project.

The Energy Code's purpose, dating to the first Building Energy Efficiency Standards adopted in 1978, is to reduce wasteful and unnecessary energy consumption in buildings. For an HVAC contractor, that translates into two things nearly every job touches: (1) installed equipment must meet minimum efficiency ratings, and (2) many installations must be field-verified by an independent third party (covered in Section 9.2).

Two Compliance Paths

Title 24 Part 6 compliance can be demonstrated through two different paths:

• Prescriptive compliance -- the project follows a fixed checklist of minimum requirements (equipment efficiency, duct insulation, control settings) with no energy modeling required.
• Performance compliance -- CEC-approved energy modeling software calculates whether the "proposed" building's total energy use is no worse than a "standard" reference building built to code minimums. This path offers more design flexibility -- for example, trading a lower-efficiency furnace for better duct sealing and envelope performance -- but requires access to approved compliance software and a qualified preparer.

Either path produces the CF1R Certificate of Compliance (covered fully in Section 9.4), which the HVAC contractor commonly prepares and submits alongside the permit application for equipment-only scope of work.

Minimum Equipment Efficiency

Title 24 references, and layers additional state-specific requirements on top of, federal Department of Energy (DOE) minimum efficiency standards. Since 2023, those federal minimums are expressed using the SEER2 / EER2 / HSPF2 metrics -- a revised laboratory test procedure (called M1) that typically yields ratings a few percentage points lower than the older SEER/HSPF numbers for the exact same physical piece of equipment. A contractor should never assume an older "SEER 14" nameplate automatically satisfies a current "SEER2" minimum -- always check the unit's current CEC- or AHRI-certified rating rather than relying on a legacy label.

Baseline minimums a C-20 contractor commonly encounters when bidding standard residential replacement work include:

These figures reflect the federal efficiency floor referenced by the current code cycle; because both DOE and CEC standards can be revised, a contractor should confirm the specific number against the equipment's current listing before finalizing a bid rather than treating any number memorized today as permanent.

Beyond the nameplate efficiency rating, the 2025 Energy Code cycle added several HVAC-specific mandatory measures that a C-20 contractor must build into every applicable bid:

• Duct leakage is capped at 5% for new single-family construction (Section 9.2 covers the full leakage table, including the looser thresholds that apply to alterations).
• Ducts run through conditioned space now require a minimum R-6.0 insulation value.
• Airflow and fan efficiency testing is mandatory on all newly installed HVAC systems.
• Heat pump refrigerant charge now requires third-party HERS verification in every California climate zone -- not just a subset of zones, as under earlier cycles.
• Heat pump water heaters are now the prescriptive baseline for residential water heating, even in additions, and the prescriptive space-conditioning baseline points toward heat pumps statewide, with limits on electric-resistance backup heat (commonly a lockout above roughly 35 degrees Fahrenheit outdoor air temperature) to prevent inefficient operation of backup strips.

Climate Zones and Why They Matter

Because California spans coastal fog belts, hot inland valleys, low desert, and alpine terrain within a single state, one statewide efficiency requirement would be too loose in some regions and too strict in others. The CEC divides California into 16 Building Climate Zones (CZ1 through CZ16), each carrying its own "energy budget" derived from historical temperature, humidity, solar radiation, and elevation data recorded at a representative weather station for that zone. Every jurisdiction is assigned to exactly one climate zone, and that zone assignment drives the prescriptive envelope, duct, and HVAC package requirements that apply to a specific project.

The zones vary enormously. Climate Zone 15 (low desert, including the Coachella and Imperial Valleys) carries extreme cooling loads and minimal heating demand, while Climate Zone 16 (high mountain areas, including parts of the Sierra Nevada and northeastern California) carries extreme heating loads and comparatively little cooling demand. Mild coastal zones (such as CZ3 and CZ5) sit between these extremes in both directions. A system correctly sized and specified for CZ15 would be badly wrong for CZ16, and the reverse is equally true -- climate-zone misidentification is one of the most common causes of both Title 24 compliance failures and comfort complaints found in the field.

C-20 exam candidates should also know that a climate zone is not simply the same thing as a ZIP code or county boundary -- jurisdiction lines do not always follow natural climate boundaries, so the zone must be looked up in the CEC's official climate zone finder or confirmed within compliance software, not assumed from a mailing address. For estimating and load-calculation purposes (see Chapter 8), the climate zone assignment is one of the very first inputs a contractor pulls before running a Manual J load calculation or completing a CF1R, because it sets both the outdoor design temperature used in the load calculation and which prescriptive HVAC package the project must satisfy.