A federal court has upended the core legal strategy natural gas supporters have relied on to preserve gas-powered appliances in homes and businesses.

In recent years, both advocates and opponents of natural gas appliances have had their day in court, but this time opponents secured a major win.

The case, Rinnai America Corp. v. South Coast Air Quality Management District (SCAQMD), was heard in July before the U.S. District Court for the Central District of California. At issue was whether a local air pollution control agency has the authority to enact an emissions rule that effectively bans gas-powered appliances. On July 18, the court answered: yes, the agency does have that authority.

The dispute stems from a 2024 SCAQMD rule that set a zero-NOx emission limit for large water heaters, boilers, and process heaters. In June 2024, SCAQMD amended an earlier emissions rule to require zero emissions for large water heaters, boilers, and process heaters, phased in between 2026 and 2033. The rule also covers pool and spa heaters rated between 75,000 and 2 million BTU/hour — an estimated 710,000 residential units — meaning that new or replacement systems will need to be electric heat pumps.

SCAQMD justified the rule as necessary to reduce pollution in Southern California, a region long plagued by some of the nation’s worst air quality.

According to SCAQMD, the rule is expected to cut NOx emissions by 5.6 tons per day — roughly 10 percent of the reductions needed for the region to meet federal ozone standards. Since its creation in 1977, the district has been legally required to meet federal smog and soot standards, and the amended rule was presented as essential to that mission.

Environmental and public health groups praised the decision, highlighting the health benefits of reduced smog and pollutants. Organizations such as the Sierra Club and Earthjustice argue that gas appliances are a major but often underestimated source of pollution.

Opponents, however, warn of steep costs and logistical hurdles for manufacturers, businesses, and consumers. Concerns include costly retrofits, strain on the electrical grid, and a patchwork of local regulations. Groups such as Heating, Air-conditioning, & Refrigeration Distributors International (HARDI) maintain that existing standards are sufficient, since SCAQMD already meets federal and state NOx thresholds. They argue the new rule is unnecessary and will deliver minimal benefits.

But these arguments were not directly at issue in Rinnai America Corp. v. SCAQMD. The court instead considered whether the district has the authority to impose emission limits that, in effect, ban gas-powered appliances.

Rinnai’s legal team claimed that SCAQMD’s rule was invalid because it was “preempted” by the federal Energy Policy and Conservation Act (EPCA), which prevents state or local governments from passing laws that conflict with federal energy regulations — a line of reasoning that courts have accepted in other cases.

That argument was bolstered in April 2023, when the Ninth Circuit Court of Appeals struck down Berkeley’s ordinance banning natural gas piping in most new buildings (California Restaurant Association v. Berkeley).

The ordinance was highly controversial because, if allowed to stand, it would have effectively eliminated the installation of gas stoves, cooktops, ovens, and other appliances in new construction— impacting both homeowners who prefer cooking with gas and restaurants that rely on it for their business. The court ruled that Berkeley’s ban improperly regulated “energy use,” a domain reserved for the federal government under EPCA. Because the ordinance blocked the use of gas appliances, it conflicted with federal energy efficiency standards, which assume natural gas as a permitted fuel source.

Following the Berkeley ruling, several cities within the Ninth Circuit’s jurisdiction — including Santa Barbara, San Luis Obispo, and Eugene, Oregon — repealed their natural gas bans. At the state level, Washington delayed new building codes requiring heat pumps, citing the decision. Even outside the Ninth Circuit, such as in New York, the preemption argument was raised, though ultimately rejected by local courts.

In the present case, however, the California federal court rejected the preemption argument, siding with SCAQMD’s authority to impose the zero-NOx rule.

That outcome marks a significant setback for natural gas supporters, who had relied heavily on preemption as a winning legal strategy.

The plaintiffs — Rinnai and its coalition — have appealed the district court’s July 18, 2025 ruling to the Ninth Circuit Court of Appeals. Given that the Ninth Circuit already set a precedent in the Berkeley case, this appeal is pivotal. The appellate court’s familiarity with EPCA preemption makes it a central battleground.

In their appeal, the plaintiffs are likely to argue once again that the zero-NOx rule, although presented as an emissions regulation, is in effect a ban on gas appliances, and therefore subject to preemption under the Energy Policy and Conservation Act — just as the Berkeley ordinance was. The South Coast Air Quality Management District, in contrast, is expected to stress the key distinction that its rule regulates pollution, not energy use, and therefore falls squarely within the authority granted by the Clean Air Act. In their view, EPCA preemption simply does not apply to emissions-based rules.

Although no firm timeline has been set, Rinnai’s opening appellate brief is scheduled for late September 2025, with the district’s response expected in October.

The outcome could carry broad implications. A ruling in Rinnai’s favor may revive legal challenges to similar zero-NOx or electrification mandates across California and beyond, potentially stalling regulations in the Bay Area or even statewide. More broadly, the case highlights a growing tension between federal preemption and local authority: to what extent can local agencies pursue air quality goals that require a move away from natural gas, without intruding into areas of regulation that Congress has reserved for the federal government?

Meanwhile, in Washington, D.C., federal lawmakers are weighing whether to settle this debate nationally. Bills known as the “Energy Choice Act,” introduced in June 2025 by Rep. Nick Langworthy (H.R. 3699) and Sen. Jim Justice (S. 1945), would bar states and localities from banning or restricting specific energy sources. If passed, the law would effectively preempt local gas bans and electrification mandates, halting many of the kinds of regulations now being litigated in California. An earlier version of the bill stalled in the last Congress, but its reintroduction underscores the rising national stakes of the gas wars.