Mini-split Title 24 requirements under the 2025 Energy Code

A ductless mini-split can meet California's Title 24 energy rules, and it is the most common choice for ADUs and garage conversions. Under the 2025 Energy Code, it must be sized from a load calculation, and an ECC rater (formerly HERS rater) must verify its refrigerant charge in every climate zone.

These rules apply to permit applications submitted on or after January 1, 2026. Sources are the 2025 Energy Code, Chapter 4 of the CEC's Single-Family Compliance Manual and the CEC's ADU FAQ.

Is a mini-split allowed under Title 24?

Yes. The CEC's ADU FAQ says ADUs can use a mini-split or multi-split system. Every system must meet:

  • The appliance efficiency rules in Section 110.2.
  • The mandatory equipment rules in Section 150.0(h).
  • The other parts of Sections 150.0, 150.1 and 150.2 that fit your project (new home, addition or alteration).

How must a mini-split be sized?

Section 150.0(h) sets the method:

  • Loads. Heating and cooling loads must be based on the ASHRAE Handbook, the SMACNA residential manual or ACCA Manual J. For additions, block loads (all rooms combined) may be used.
  • Indoor design temperatures. 68°F for heating and 75°F for cooling.
  • Outdoor design temperatures. From Joint Appendix JA2, the ASHRAE Handbook or Manual J, no more extreme than the 99.0 percent heating and 1.0 percent cooling values.
  • Equipment selection. Systems "shall be sized based on ACCA Manual S-2023."
  • Heat pump heating capacity. It must meet the minimum heating rules of the California Building Code, without counting supplementary heat. There is no maximum.
  • Cooling capacity. There is no limit on the minimum capacity.

Additions. The 2025 code adds maximum capacity tables for systems serving additions (Section 150.2(a)1E). Exception 1 to that rule exempts ductless space-conditioning systems.

What does the Energy Code require during installation?

Several mandatory items in Section 150.0(h) apply to most mini-splits:

  • Dryer vent clearance. The outdoor unit must be at least 5 feet from the outlet of any dryer vent.
  • Liquid line drier, if the manufacturer's instructions call for one.
  • Defrost timer. If the heat pump has an installer-adjustable defrost delay timer, it must be set to 90 minutes or more, and the installer certifies the setting on the CF2R. Climate zones 6 and 7 are exempt. So are dwellings of 500 square feet or less in zones 3, 5 through 10 and 15.
  • Supplementary heat lockout. If the system has backup heat, such as electric strips, it must lock out above an outdoor temperature of no more than 35°F, with some exceptions for small buildings.

Why does a mini-split need refrigerant charge verification?

Section 150.1(c)7A requires it, and the compliance manual says mini-split systems need it "in all climate zones." Wrong charge, too much or too little, lowers efficiency and can damage the compressor.

The code gives two routes:

  • Systems that can use the standard test. These need measurement access holes and verified airflow, and the rater checks charge with the standard procedure in Reference Appendix RA3.2.2.
  • Systems that cannot. Many mini-splits fall here. The installer charges by weight (the weigh-in procedure in RA3.2.3.1), and an ECC rater verifies it under RA3.2.3.2.

The manual is specific: for systems "such as some mini-split systems," verification "can be accomplished only by simultaneous observation of the installer's weigh-in." The CEC's single-family refrigerant charge verification form (CF3R-MCH-25-H) says the rater "Must Observe and Confirm All Data Collected." So the rater must be on site the day the installer charges the system.

What else does the ECC rater check on a mini-split?

The CEC's ADU FAQ lists common items:

  • Refrigerant charge (all climate zones)
  • Verified SEER2 (cooling efficiency)
  • Verified HSPF2 (heating efficiency)
  • Verified heat pump rated heating capacity
  • Minimum airflow
  • Duct leakage and fan watts per cfm, for ducted systems only

Which ones apply depends on your report. Verified ratings often appear when the performance model takes credit for efficient equipment. Your CF1R's ECC section is the exact list. For visit counts and scheduling, see ECC (HERS) rater testing for an ADU.

Are there extra rules for variable-capacity mini-splits?

Only if your report takes that credit. The compliance manual's variable capacity heat pump (VCHP) option for ductless systems requires:

  • All indoor units entirely in conditioned space.
  • Wall-mounted thermostats in zones over 150 square feet.
  • Airflow to all habitable spaces.
  • Refrigerant charge verification.

If your CF1R lists VCHP verifications, place the heads and thermostats to match.

Can my ADU share the main house's ducted system instead?

No, if the ADU is a separate dwelling. The CEC says the California Mechanical Code does not allow return air from one dwelling to be sent into another through a forced-air system. That is one reason most ADUs get their own mini-split. See Title 24 for ADUs.

What paperwork does the installer sign?

The HVAC contractor signs install forms (CF2Rs) in the registry, for example refrigerant charge (CF2R-MCH-25) and rated equipment (CF2R-MCH-26) when the CF1R lists them. The rater then signs the matching CF3Rs. See CF1R, CF2R and CF3R explained.

Need a report for your mini-split project? See our flat prices.

Frequently asked questions

Can I use a ductless mini-split to meet Title 24?

Yes. The CEC's ADU FAQ confirms mini-splits and multi-splits can be used. They must meet the equipment efficiency rules in Section 110.2, the mandatory rules in Section 150.0(h), and the other sections that apply to new construction or additions.

Does a mini-split need a HERS or ECC rater?

Usually, yes. Refrigerant charge verification is required for heat pumps, including mini-splits, in every climate zone. Your CF1R may also list verified SEER2, HSPF2 and heating capacity.

Why does the rater have to be there when the mini-split is charged?

Most mini-splits cannot be checked with the standard charge test. The Energy Code then requires the installer's weigh-in to be verified by an ECC rater, and the compliance manual says that can only be done by watching the weigh-in as it happens.

How must a mini-split be sized?

Heating and cooling loads must be calculated with ASHRAE, SMACNA or ACCA Manual J methods, and equipment must be selected under ACCA Manual S-2023. For heat pump heating, there is no maximum capacity limit.

Does a mini-split in an addition have a maximum size?

No. The 2025 code adds maximum capacity limits for systems in additions, but Exception 1 to Section 150.2(a)1Eii exempts ductless systems.

Related

Sources

  1. energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/energy-code-support-center-6/2025
  2. energy.ca.gov/sites/default/files/2026-07/CEC-400-2025-010-F.pdf
  3. energy.ca.gov/filebrowser/download/8636?fid=8636
  4. energy.ca.gov/filebrowser/download/8282?fid=8282
  5. energy.ca.gov/sites/default/files/2025-07/CEC-400-2025-010-AP.pdf
  6. energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/2025-building-energy-efficiency-3