Impact Analysis: 2025 Update to the California Energy Code

This report describes the estimated impacts on energy use, grid demand, and emissions resulting from the adoption of the 2025 Energy Code (California Code of Regulations, Title 24, Part 6). The 2025 Energy Code was adopted by the California Energy Commission (CEC) in August 2024 and went into effect on January 1, 2026. The analysis in this report compares the prescriptive and mandatory requirements of the 2022 and 2025 Energy Codes using prototypical energy models in 16 California building climate zones. The analysis accounts for interactive effects between changes in requirements, such as how modifications to the building envelope influence heating and cooling loads. The analysis estimates savings in terms of site energy (kWh and therms), long-term system cost (LSC), hourly source energy (HSE), annualized grid demand (AGD), and greenhouse gas (GHG) emissions resulting from the 2025 Energy Code for the residential, multifamily, and nonresidential building sectors.