Regulation 9 Rule 6: Nitrogen Oxides Emissions from Natural Gas-Fired Water Heaters - 2023 Amendment (Current)

Learn about the Air District's rule amendment process seeking to reduce emissions of nitrogen oxides from residential and commercial water heaters in buildings in the Bay Area through changes to Regulation 9, Rule 6.

Find out about the status and anticipated timeline of the rule development process. Information on hearings, workshops, and other events is provided below, along with supporting documents and materials.

Background and Resources: 

Staff recently developed a new "Know the Facts" website to house helpful background information related to the building appliance rules.

Below is a summary of the recent milestones:

• -In July 2026, staff released draft rule language and an accompanying preliminary staff report for potential amendments to Rule 9-6.
• -In May 2026, staff presented updated concepts for flexibility amendments to Rule 9-6. The May 6th meeting ended early due to loss of quorum. The meeting will be continued on May 13, 2026 to receive Board member comments. This session will not include a public comment period.
• -In February 2026, staff presented an informational update to the Stationary Source Committee. Staff presented information about options for defining low-income qualified exemptions. 
• -In December 2025, staff presented to the Stationary Source Committee. A summary of the comments received on the Concepts Paper were presented at the December 10th Stationary Source Committee.
• -In October 2025, staff released a Concepts Paper for public review and consideration along with a 30-day public comment period. 

Background and Resources: New Supporting Documents

• New Myths vs Facts Sheet(159 Kb PDF, 2 pgs, revised 7/14/2026) (Updated July 2026)
• Frequently Asked Questions for Rules 9-4 and 9-6(607 Kb PDF, 5 pgs, revised 7/14/2026) (Updated July 2026)
• Fact Sheet - Proposed Amendments to Rules 9-4 and Rule 9-6 (177 Kb PDF, 1 pg, revised 7/14/2026)(Updated July 2026)
• Water Heater Rule Draft Amendments Overview(304 Kb PDF, 2 pgs, posted 7/17/2026)( Tagalog | tiếng Việt | Español | 中文 ) (New July 2026) 

Rule Development History

In 2023, Air District staff developed amendments to Rule 9-6: Nitrogen Oxides Emissions from Natural Gas-Fired Boilers and Water Heaters and Rule 9-4: Nitrogen Oxides from Fan Type Residential Central Furnaces. 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.

Amendments to Regulation 9: Inorganic Gaseous Pollutants, Rule 6: Nitrogen Oxides Emissions from Natural Gas-Fired Boilers and Water Heaters (Rule 9-6) were adopted by the Air District Board of Directors at a public hearing on March 15, 2023, along with amendments to Rule 9-4.

-Regulation 9: Inorganic Gaseous Pollutants, Rule 6: Nitrogen Oxides Emissions From Natural Gas-Fired Boilers and Water Heaters (Amendments Adopted 3/15/2023)(186 Kb PDF, 6 pgs, revised 3/23/2023)
(878 Kb PDF, 54 pgs, posted 3/7/2023)

-Final Staff Report for Proposed Amendments to Rule 9-4 and Rule 9-6 (878 Kb PDF, 54 pgs, posted 3/7/2023)

Implementation Working Group

As part of the recent amendments, the Air District committed to convene the Implementation Working Group (IWG). The IWG for Phase 1 (water heaters) and Phase 2 (furnaces) are composed of over 40 invited stakeholders representing a variety of stakeholder segments.

The purpose of the IWG is to provide input to Air District staff’s periodic reports to the Board of Directors on the implementation of the Building Appliances Rules and to provide the Air District staff with insights on the technical readiness of the market and equitable transition to compliant appliances, so as to not unduly burden any income class or professional group. As such, the IWG provides a forum for invited members to discuss technical and equity aspects of implementing the Building Appliances Rules.

The IWG meetings for Phase 1 took place virtually via Zoom in 2023 and 2024. The IWG meeting for Phase 2 began in October 2025 and will also take place virtually via Zoom. Members of the public are able to attend in listen-only mode with the opportunity to provide public comments at the end of the meeting. Additional information can be found on the Implementation Working Group webpage.

Adoption of Amendments to Rule 9-4 and Rule 9-6

The Air District hosted a public workshop on October 7, 2021 to discuss initial outcomes from the Building Appliance Stakeholder Working Group and first draft language of regulatory amendments. Staff provided updates to the Stationary Source and Climate Impacts Committee through 2021 and 2022. In May of 2022, the Air District released a Notice of Preparation (NOP) of an Environmental Impact Report (EIR) and an Initial Study, as well as revised draft rule amendments.

The Air District released a Notice of Public Hearing, California Environmental Quality Act (CEQA) Notice of Availability, CEQA Draft EIR, proposed amendments to Rules 9-4 and 9-6, Staff Report, and other supporting materials in December 2022 and accepted written public comments on these materials. The Air District released the Final Proposal Package, including the proposed amendments to Rules 9-4 and 9-6, Final Staff Report, CEQA Final EIR, and Response to Comments.

• Frequently Asked Questions – Adopted Amendments to Rules 9-4 and 9-6(664 Kb PDF, 5 pgs, posted 1/30/2025)
• Fact Sheet – Proposed Amendments to Rules 9-4 and 9-6(238 Kb PDF, 1 pg, posted 1/30/2025)
• Infographics – Proposed Amendments to Rules 9-4 and 9-6(115 Kb PDF, 1 pg, posted 3/16/2023)
• Notice of Public Hearing and Notice of Availability of DEIR(268 Kb PDF, 2 pgs, posted 12/19/2022)
• Final Environmental Impact Report for Proposed Amendments to Rule 9-4 and Rule 9-6(9 Mb PDF, 184 pgs, posted 3/7/2023)
• Staff Report – Proposed Amendments to Building Appliance Rules – Regulation 9, Rule 4 and Rule 6(878 Kb PDF, 54 pgs, posted 3/7/2023)
  • Appendix A: Proposed Amendments to Rule 9-4(581 Kb PDF, 7 pgs, revised 12/20/2022)
  • Appendix B: Proposed Amendments to Rule 9-6(437 Kb PDF, 6 pgs, revised 12/20/2022)
  • Appendix C: Socioeconomic Impacts Analysis(1004 Kb PDF, 37 pgs, revised 12/20/2022)
  • Appendix D: Electric Infrastructure Impacts from Proposed Zero NOx Standards(1 Mb PDF, 38 pgs, revised 12/20/2022)
  • Appendix E: Assessing Ambient Air Quality and Health Impacts from Natural Gas Building Appliances in the Bay Area(5 Mb PDF, 40 pgs, posted 12/19/2022)
  • Appendix F: Exposure and Equity Assessment of Natural Gas Appliances in the San Francisco Bay Area(17 Mb PDF, 17 pgs, revised 12/20/2022)
  • Appendix G: Draft Environmental Impact Report(10 Mb PDF, 295 pgs, posted 12/19/2022)
  • Appendix H: Response to Comments(1 Mb PDF, 932 pgs, posted 3/7/2023)

The Air District Board of Directors conducted a public hearing on March 15, 2023 and adopted the proposed amendments to Rules 9-4 and 9-6 and certified the CEQA EIR. Information and a recording of the public hearing can be found on this page under 'Hearings, Workshops and Other Events'.

Rule 9-6 Implementation Report (2024)

Air District staff presented an informational update on implementation readiness of the zero NOx requirements for residential water heaters (Rule 9-6) to the Air District Board of Directors on December 4, 2024. The Board materials included a staff report summarizing information gathered during the implementation working group process, which can be found here: Staff Report - Informational Update Regarding Regulation 9, Rule 6.(1 Mb PDF, 58 pgs, posted 11/27/2024) Appendices to the staff report can be found on the Implementation Working Group webpage.

Rule 9-6 Concepts Paper (2025)

In October 2025, the Air District released a Concepts Paper for potential amendments to Rule 9-6 (Nitrogen Oxides from Natural Gas-Fired Water Heaters). These changes are focused on affordability and availability considerations. They are intended to provide additional flexibility and ensure a smooth transition as older appliances are replaced with cleaner options. The 30-day public comment period is now closed.

• Concepts Paper(6 Mb PDF, 29 pgs, posted 10/24/2025)

Regulatory Overview: Rule 9-6 Flexibility Amendments Report (May 2026)

Staff presented updated flexibility and affordability concepts to Rule 9-6 at the May 6th and May 13th Board of Directors meetings. In advance of the presentation staff released an informational document titled Regulatory Overview: Rule 9-6 Flexibility Amendments ("Regulatory Overview")  which is intended to give the public and Board members additional context on staff's process-to-date and current recommendations. 

The Regulatory Overview provides background on potential amendments to Rule 9-6, including key considerations related to exemptions, potential implementation challenges, and key factors such as income-based eligibility and building or project constraints.

The May presentations included discussions of draft concepts related to the potential amendments to the zero NOx requirements in Rule 9-6 for small water heaters and staff’s recommendations. The concepts were last discussed at the February 2026 Stationary Source Committee meeting. The May 6th meeting included a dedicated time for public comment, the May 13th meeting was a continuation of the previous one due to loss of quorum.

Draft Regulatory Language and Preliminary Staff Report for Rule 9-6 Amendments (July 2026)

Staff have released draft regulatory language and an Updated Regulatory Overview report for flexibility amendments to Rule 9-6 addressing small water heaters (<75,000 BTU/hour). The documents can be found below:

• Draft Regulatory Language (232 Kb PDF, 11 pgs, revised 7/14/2026)
• Updated Regulatory Overview(1 Mb PDF, 39 pgs, revised 7/14/2026)

Hearings, Workshops and Other Events

Throughout the rule development process, we provide information on upcoming and past workshops, hearings, and other events.

Documents

Supporting materials, such as staff reports, regulatory language, and other technical documents related to rule development, are posted throughout the development process.

Comments

The Air District provides opportunities for the public to submit comments throughout the development process, and posts comments received during the open public comment periods.