Mandatory Requirement Updated Guidance
Section 120.6(d)3 of the 2022 and 2025 Energy Codes require process boilers with an input capacity greater than 5 million Btu/h (British Thermal Units per Hour) to maintain stack-gas oxygen concentrations less than or equal to 3% by volume on a dry basis for firing rates from 20% to 100%. Boilers with steady state full-load combustion efficiency 90% or higher are exempt from this requirement. Concurrently, air districts in California limit emissions from process boilers, including emissions of oxides of nitrogen (NOₓ). These emission requirements may vary by air district.
Several interested members of the public have submitted comments to the California Energy Commission (CEC) expressing concerns that process boilers may not meet both the stack-gas oxygen concentration requirements in the 2022 and 2025 Energy Code and the NOₓ emission limits set by some air districts. This is because the practice and technologies used to reduce NOₓ emissions typically result in higher stack-gas oxygen concentrations. CEC staff investigations confirmed these concerns. Therefore, CEC staff are issuing updated guidance.
The CEC advises that when the 2022 or 2025 Energy Codes conflict with the federal Clean Air Act, the federal Clean Air Act takes precedence. Therefore, CEC staff recommend that enforcement agencies prioritize air district emission standards when it is not possible to comply with both the Energy Code’s stack-gas oxygen concentrations requirements and air district emission standards at the same time.
Further Information
Questions about this guidance or the Building Energy Efficiency Standards in general may be directed to the Energy Code Hotline Submission Form.