Title
HEARING - Air Quality Management District (AQMD) recommending the Board, acting as the AQMD Board of Directors:
1) Adopt and authorize the Chair to sign Resolution 141-2025, approving the amendments to Rule 239, Natural Gas-Fired Water Heaters Less than 1,000,000 BTU per Hour; and
2) Direct staff to forward the rule to the California Air Resources Board for transmittal to the U.S. Environmental Protection Agency as a revision to the State Implementation Plan.
FUNDING: N/A
Body
DISCUSSION / BACKGROUND
The Sacramento Federal Nonattainment Area (SFNA) comprises Sacramento and Yolo Counties, the western portion of El Dorado and Placer Counties, the southern portion of Sutter County, and the northeastern portion of Solano County. AQMD is the agency responsible for maintaining the National Ambient Air Quality Standards (NAAQS) in El Dorado County.
Ozone is formed when volatile organic compounds (VOCs) and nitrogen oxides (NOx) undergo photochemical reactions in the presence of sunlight. In 2009, the AQMD Board and the Boards of other SFNA air districts approved the 1997 SFNA 8-hour Ozone Attainment and Reasonable Further Progress Plan (Plan), with revisions adopted in 2011 and 2013. This Plan demonstrates how existing and new control strategies will provide the necessary emission reductions to meet Clean Air Act (CAA) requirements for attainment of the 1997 8-hour ozone NAAQS. To achieve the additional reductions needed, the Plan included new control measures to be incorporated into the SIP. As part of these SIP commitments, the SFNA air districts agreed to adopt various control strategies and rule updates. Specifically, the Plan included a commitment for the AQMD to achieve NOx emission reductions from a water heater control measure within the heat input range of 75,000 to 1,000,000 Btu/hr.
The ozone NAAQS were first established in 1979 as a 1-hour standard. They were later revised to 8-hour standards in 1997, 2008, and 2015. The 1997 8-hour ozone NAAQS was set at 80 parts per billion (ppb) (62 FR 38856, July 18, 1997). The SFNA was designated as a nonattainment area with a Severe-15 classification under the 1997 8-hour ozone NAAQS. The U.S. Environmental Protection Agency (EPA) has since revoked the 1997 standard for purposes of new designations; however, areas previously designated as nonattainment under this standard remain subject to CAA requirements, including SIP commitments, until those obligations are satisfied and the area is formally redesignated to attainment (75 FR 29361, May 25, 2010).
Additionally, under CAA section 107(d)(3)(E)(iii), an area may only be redesignated to attainment if it demonstrates that air quality improvements are the result of permanent and enforceable emission reductions from implementation of the approved SIP. CAA section 107(d)(3)(E)(v) also requires that the area has met all applicable requirements of CAA Part D for nonattainment areas, including section 172(c)(1) and (6), which mandate implementation of reasonably available control measures and other enforceable emission limitations. Together, these provisions require that all nonattainment area requirements addressed in a SIP revision, including commitments to revise enforceable emission limitations in District rules, be fully implemented before EPA can approve redesignation to attainment.
The current version of Rule 239, adopted in 1998, limits NOx emissions for new residential water heaters with a heat input capacity of less than 75,000 Btu/hr to 40 nanograms per joule (ng/J), and to 50 ng/J for mobile home water heaters. The AQMD committed to implementing a new control measure establishing a NOx emission standard of 14 ng/J (20 ppmv at 3% O2) for units rated ≥75,000 Btu/hr and <1,000,000 Btu/hr. However, for water heaters used to heat pools and spas with a rated heat input capacity of 400,000 Btu/hr or less, the control measure sets a less stringent limit of 40 ng/J (55 ppmv at 3% O2). The new standards will be effective as of the effective date of the EPA's final action approving the rule.
The U.S. Department of Energy classifies residential gas water heaters as units with an input capacity of 75,000 Btu/hr or less. Accordingly, the term “residential” was removed from Rule 239 to avoid unnecessary repetition, and the rule was expanded to apply to units with heat input capacities greater than 75,000 Btu/hr.
Existing equipment will not be subject to the proposed changes. The new emission limits will apply only when existing units are replaced.
A public notice was published in the Tahoe Daily Tribune and Mountain Democrat on September 19, 2025, initiating a 30-day public comment period. The public notice and proof of publication are attached. AQMD has not received any comments during the public comment period regarding the proposed changes to Rule 239.
AQMD staff recommends the Board conduct a public hearing, approve the resolution, and adopt Rule 239, Natural Gas-Fired Water Heaters Less than 1,000,000 BTU per Hour. If approved, the rule will be forwarded to CARB and the EPA for inclusion in the State Implementation Plan.
ALTERNATIVES
The Board of Directors may wholly approve, deny, or make further revisions to the proposed rule.
PRIOR BOARD ACTION
N/A
OTHER DEPARTMENT / AGENCY INVOLVEMENT
County Counsel approved the Resolution
CAO RECOMMENDATION
Approve as recommended.
FINANCIAL IMPACT
No financial impact to AQMD, the County or sources operating in the County.
CLERK OF THE BOARD FOLLOW UP ACTIONS
1) Clerk to obtain the Board Chair's signature on three (3) original Resolutions, and
2) Clerk to provide AQMD with two (2) signed copies of the Resolution to be forwarded to the California Air Resources Board.
STRATEGIC PLAN COMPONENT
N/A
CONTACT
Rania Serieh, Air Pollution Control Officer