When did the 2025 Title 24 Part 6 take effect?

The 2025 California Energy Code (Title 24 Part 6) took effect for permit applications submitted on or after January 1, 2026. Projects with permit applications dated before that retain the 2022 standards through their construction lifecycle.

Does Title 24 2025 require heat pumps in California commercial buildings?

Title 24 2025 sets heat pumps as the prescriptive baseline for space-heating and water-heating in most commercial building types. Gas-fired heating remains permissible but moves into the performance compliance path, where it must be offset elsewhere in the energy budget. For most TI scope, the practical effect is heat pumps win.

What refrigerant GWP limits apply under Title 24 2025?

California's CARB Refrigerant Management Program (separate from Title 24 but parallel-tracked) restricts new commercial HVAC equipment to refrigerants with GWP-150 or lower starting January 1, 2026. The dominant compliant refrigerants are R-454B and R-32. R-410A is being phased out of new commercial equipment manufacture.

Is demand-controlled ventilation required by Title 24 2025?

Yes - DCV is required for high-density occupancy zones (offices over 500 sq ft per zone with design occupancy above 25 people per 1,000 sq ft, classrooms, conference rooms, fitness rooms) under Title 24 § 120.1(d). CO2 sensors are the standard sensing mechanism, modulating outside-air dampers to meet ASHRAE 62.1 per-person requirements rather than design max.

What HERS verifications are required on commercial mechanical work?

Title 24 2025 requires HERS verification for: duct leakage (NC ducts in unconditioned space, 6% leakage limit), refrigerant charge verification, fan efficacy on small commercial systems, and demand-controlled ventilation sensor calibration. A CEC-certified HERS rater is engaged separately from the mechanical contractor; the mechanical contractor builds for verifiable compliance.

Energy Code · Compliance · Published 2026-05-28

Title 24 mechanical code 2025 - what changed for California commercial buildings

The 2025 California Energy Code (Title 24 Part 6) took effect January 1, 2026. For general contractors, property managers, and facility directors with active California projects, here are the mechanical-scope changes that actually move on submittal sets, equipment selection, and TI schedules.

What Title 24 Part 6 governs

Title 24 Part 6 - the California Energy Code - is California's commercial and residential building energy-efficiency standard. It is updated on a three-year cycle by the California Energy Commission (CEC). Part 6 sits alongside the California Building, Mechanical, Plumbing, Electrical, Fire, Green Building (CALGreen) codes - all in Title 24 - but Part 6 is the one that drives mechanical equipment selection, ventilation strategy, controls, and HERS verification.

The 2025 cycle is the most aggressive electrification push California has codified to date. It is meant to align with the state's 2045 carbon-neutrality goal and the CARB refrigerant-management program.

1. Heat pumps as the prescriptive baseline

Under Title 24 2025, electric heat pumps are the prescriptive compliance default for most commercial space-heating and service-water-heating applications. Gas-fired systems are not banned, but they move into the performance-compliance pathway: the design must demonstrate equivalent or better TDV (time-dependent valuation) energy performance than the all-electric baseline.

Practical impact:

Replacement-in-kind projects (gas RTU swap) become harder to justify - the energy modeling must offset elsewhere.
New construction and ground-up TI projects are easier to spec as heat-pump packaged units (Daikin Rebel, Trane Voyager Coil-on-Coil, Carrier WeatherExpert, AAON M-Series).
VRF systems get a tailwind: they were already attractive for multi-zone TI; now the energy model rewards them more.

2. Refrigerant GWP limits (CARB-driven, Title 24-adjacent)

California's CARB Refrigerant Management Program imposes a GWP-150 limit on new commercial HVAC equipment sold or installed in California starting January 1, 2026. The legacy refrigerants R-410A and R-407C exceed that limit and are being phased out of new equipment manufacture.

Compliant refrigerants:

R-454B (GWP ≈ 466 - California allows up to GWP-700 for some categories; check current CARB tables) - adopted broadly by Carrier, Trane, Lennox, Daikin Applied.
R-32 (GWP ≈ 675) - adopted broadly by Daikin, Mitsubishi.
R-290 (propane) and CO2 (R-744) in specialty applications.

R-454B and R-32 are mildly flammable (A2L classification under ASHRAE 34). California Mechanical Code now requires leak-detection sensors in occupied spaces above certain refrigerant charge thresholds, and refrigerant-detection-interlock controls on the airflow. Service-technician certification (EPA 608 + manufacturer A2L-specific training) is mandatory.

3. Fan efficacy and motor efficiency

Title 24 § 140.4(c) tightens fan-system efficacy limits. For commercial HVAC fans over 1 hp, the required fan electrical power index (FEI) is now 1.00 or better for most applications, with stricter limits on small high-volume fans where energy waste is concentrated. ECM (electronically commutated motor) drives are effectively required on terminal-unit fans and parallel-fan-powered boxes.

In practice, this kills the use of legacy PSC (permanent split-capacitor) motor terminal units. Specify ECM throughout, and check your VAV box submittals.

4. Demand-controlled ventilation (DCV) - broader trigger

Title 24 § 120.1(d) expanded DCV requirements in 2025. The trigger thresholds for required DCV (CO2 sensors modulating outside-air dampers to ASHRAE 62.1 per-person requirements rather than design max) now include:

Office zones over 500 sq ft with design occupancy above 25 people per 1,000 sq ft.
Conference rooms, classrooms, lecture halls.
Fitness rooms, locker rooms, multi-purpose rooms.
Restaurant dining areas (new in 2025).

The CO2 sensors must be HERS-verified for calibration at commissioning and at routine intervals afterward. Most projects use Belimo, ProductLine Solutions, or Setra sensors integrated with the building management system.

5. Economizers - wider applicability

Title 24 § 140.4(e) lowered the air-side economizer trigger threshold to ≥33,000 Btu/hr cooling capacity for most California climate zones, down from 54,000 Btu/hr in prior cycles. Most rooftop units 3 tons and larger now require an economizer. Water-side economizers are required on hydronic systems above certain capacity in select climate zones.

The economizer high-limit setpoint and changeover logic must follow CEC-listed default values unless the design engineer documents an alternative - fixed-dry-bulb is permitted only in CZ 1–6, differential-enthalpy or differential-dry-bulb is required elsewhere.

6. HERS verifications - what the rater actually checks

Title 24 2025 retains the HERS (Home Energy Rating System - also applies to commercial) third-party verification requirement for:

Duct leakage - 6% total leakage limit for systems with ducts in unconditioned space.
Refrigerant charge verification on split-system replacements.
Fan efficacy testing on small commercial systems.
Economizer-control verification.
DCV sensor calibration verification.

The mechanical contractor's job is to install for verifiability: accessible test ports, accessible refrigerant-service valves, documented setpoints, calibrated commissioning. The HERS rater is hired by the project owner and tests after rough-in (duct leakage) and after start-up (charge, fan, controls).

What this means for an active California TI project

Equipment selection: default to heat pumps with R-454B or R-32 refrigerant. Lock the equipment selection at design-assist; don't wait for shop drawings.
Controls scope: add CO2 sensors and DCV control logic to the controls submittal. Coordinate with the BMS contractor early.
Service access: design for HERS testing access - test ports, accessible service valves, accessible sensors. The rater will not call back if the test fails the first time.
Schedule: HERS commissioning sits on the critical path. Add 1–2 weeks to closeout for HERS verification and re-test if needed.
Refrigerant tech certification: confirm your mechanical sub's techs hold EPA 608 + A2L manufacturer training before scheduling start-up. Many small subs do not, in early 2026.

Working with Sierra Mechanical on Title 24 2025 scope

Our PMs sit on the Title 24 mechanical compliance package for every commercial project we bid. We have EPA-608 + A2L-certified install techs across California, in-house controls coordination experience with Belimo, Honeywell, Schneider, and Distech, and a HERS-rater roster we coordinate with routinely.

For active projects: request a bid with your architectural floor plan and intended occupancy, and we can return a Title 24-compliant mechanical scope within 5 business days. Bid desk: (916) 638-8605.

References used in this article: California Energy Code (Title 24 Part 6, 2025 edition) §§ 120.1, 140.4; California Building Energy Efficiency Standards Compliance Manual (CEC, 2026); CARB Refrigerant Management Program; ASHRAE Standard 34; ASHRAE Standard 62.1. Information current as of 2026-05-28. Refrigerant GWP figures rounded per IPCC AR6.

This article is general guidance and does not constitute engineering advice for a specific project. Always work with a licensed mechanical engineer and a CEC-certified HERS rater for project-specific compliance.