TO: Napa County Climate Action Committee
FROM: Brian D. Bordona, Director of Planning, Building, and Environmental Services
REPORT BY: Ryan Melendez, Planner II, Sustainability
SUBJECT: Presentation on Bay Area Air District’s Rules 9-4 and 9-6, relating to emissions reduction of nitrogen oxides from residential and commercial furnaces and water heaters in buildings in the Bay Area
RECOMMENDATION
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Receive a presentation on the Bay Area Air District’s Rules 9-4 and 9-6, relating to emissions reduction of nitrogen oxides from natural gas-fired furnaces and water heaters in buildings in the Bay Area.
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BACKGROUND AND DISCUSSION
The Bay Area Air District’s Rule 9-6: Nitrogen Oxides Emissions from Natural Gas-Fired Boilers and Water Heaters was first adopted over thirty years ago and later amended in 2007. Rule 9-6 was established to reduce nitrogen oxide (NOx) emissions from residential water heating. Rule 9-4: Nitrogen Oxides from Fan Type Residential Central Furnaces was also originally adopted over thirty years ago and applies to small residential and commercial furnaces. Together, these rules form a key part of the Air District’s strategy to reduce emissions from buildings. In recent years, staff have been evaluating updates to both rules to reflect new technologies and support the region’s clean air and climate goals.
In March 2023, the Air District Board of Directors adopted amendments to existing Rules 9-4 and 9-6. These rules govern point of sale emission standards for small, typically residential and commercial, water and space heating systems. Emissions of nitrogen oxides impact local and regional air quality and contribute to the formation of ozone and secondary particulate matter. These requirements include zero NOx emissions standards with future implementation dates beginning in 2027, 2029, and 2031, depending on size and equipment type. These requirements apply only upon burn out of one’s current equipment. Any equipment manufactured after the new implementation date will be subject to the new standards.
In December of 2024, Air District staff presented an informational update on the implementation readiness of the zero NOx requirements for residential water heaters (Rule 9-6) to the Air District Board of Directors which was informed by an Implementation Working Group (IWG) comprised of over 40 stakeholders. Air District staff is currently working on further amendments to Rule 9-6 to address implementation and affordability concerns.
In April of 2025, Air District staff presented to the Stationary Source Committee to share proposed next steps and potential flexibilities and amendments to Rule 9-6 (2027 compliance date) based on the IWG’s findings. The second phase of the IWG is currently meeting and is focused on furnaces Rule 9-4 (2029 compliance date).
Jennifer Lam, a manager in Regulatory Development at the Bay Area Air District, will present the development processes of Rules 9-4 and 9-6 and upcoming regulatory compliance updates.
ENVIRONMENTAL IMPACT
ENVIRONMENTAL DETERMINATION: The proposed action is not a project as defined by 14 California
Code of Regulations 15378 (State CEQA Guidelines) and therefore CEQA is not applicable.