2025 Alternative Calculation Method Reference Manual

The California Energy Commission’s (CEC) 2025 Building Energy Efficiency Standards for residential and nonresidential buildings allow compliance through either a prescriptive or performance method. The performance compliance approach uses computer modeling compliance software to enable trade-offs of efficiency measures. Performance compliance is the most popular compliance method because of the flexibility it provides in building design.

Compliance software must be certified by the CEC, in accordance with the rules established for modeling compliance software. This document establishes the rules for creating a building model, describing how the proposed design is defined, explaining how the standard design is established, and outlining how compliance is reported on the performance certificate of compliance. This document also describes the procedures for performance calculation, necessary rule sets, reference method for testing compliance software accuracy, and minimum reporting requirements. The CEC reserves the right to approve vendor software for limited implementations of what is documented in this manual.

This Alternative Calculation Method (ACM) Reference Manual explains how the proposed and standard designs are determined. 

The compliance manager, public domain compliance software provided by the CEC, is called California Building Energy Code Compliance (CBECC). CBECC and all third-party compliance software must meet rules specified in the ACM Reference Manual.