California 2025 Energy Code: What Changed for Homes

California updates its Building Energy Efficiency Standards (Title 24, Part 6) every three years. The 2025 Energy Code took effect on January 1, 2026. Which code applies to your project depends on when the permit application was submitted, not when construction starts, so projects permitted in late 2025 may still be built under the 2022 rules.

The biggest visible change is a name. Under the 2025 code the field verification program is called ECC, for Energy Code Compliance, and the raters and providers are called ECC raters and ECC providers. The name change doesn't approve anyone automatically: raters are certified for a specific code cycle, and as of October 2026 CHEERS is the approved ECC provider. The job is essentially the same: an independent, certified rater tests and verifies energy measures in the field and signs the CF3R. The CEC has also tightened quality assurance and documentation requirements on providers. For homeowners and contractors, the practical point is that a permit applied for on or after January 1, 2026 uses ECC verification when the scope requires it, while an application submitted before that date stays on the 2022 code and HERS forms, even if the permit is issued in 2026. Ask your rater to confirm they are certified for your project's code cycle.

The 2022 code made heat pumps the baseline for new single-family homes, for space heating, water heating or both depending on climate zone. The 2025 code goes further: for new single-family homes, the baseline is now a heat pump for both space heating and water heating in every climate zone. For additions, when an additional water heater is installed as part of the addition, it generally has to be a heat pump water heater (small additions of 500 square feet or less also have an electric point-of-use option), and the gas tankless option the 2022 code allowed is gone. Gas equipment is still allowed in many situations, particularly when you are replacing existing gas equipment in an alteration, but in new work you generally have to compensate for it with other efficiency measures.

The 2025 code puts more emphasis on proper sizing. Heating and cooling load calculations, using a method such as ACCA Manual J, are required for new space-conditioning systems, and equipment selection now references ACCA Manual S-2023. Systems serving additions have their own sizing rules, including maximum capacity limits unless airflow is verified. For HVAC contractors that means sizing from the calculated loads, not adding an arbitrary safety margin.

Minimum wall insulation went up, to R-15 in 2x4 framing and R-21 in 2x6 framing. The prescriptive maximum window U-factor tightened from 0.30 to 0.27 in Climate Zones 1 through 5, 11 through 14 and 16, and stays at 0.30 in Climate Zones 6 through 10 and 15. New dwelling units of 500 square feet or less in Climate Zone 5 can still use 0.30. The solar heat gain limit tightened only in Climate Zone 15 for new construction. Replacement windows in alterations generally follow the same U-factor limits, and in Climate Zone 15 the replacement solar heat gain cap is 0.23. Replacements of 75 square feet or less can instead meet a U-factor of 0.40 and, in Climate Zones 2, 4 and 6 through 15, a solar heat gain coefficient of 0.35, so check the numbers for your climate zone before you order.

If you are planning an ADU, addition or new home, check the permit application date first: applications submitted on or after January 1, 2026 use the 2025 rules and software, while earlier applications stay on the 2022 code. If you are replacing HVAC equipment on a 2025-code permit, expect ECC verification for the tests your equipment, ducts and climate zone trigger. And if you are a contractor, the easiest way to avoid delays under the new code is still the old one: sealed ducts, correct charge and complete paperwork before the rater shows up, with any construction-stage inspections booked early.