On October 6, 2026, the federal minimum thermal efficiency for a commercial gas-fired storage water heater rose from 80 percent to 95 percent. That is the number in the Code of Federal Regulations, and an owner planning a replacement should specify for the rule as written, with an alternate path that does not depend on how litigation ends.
Three qualifications matter: DOE has said it will not seek civil penalties for specified gas-fired efficiency and certification obligations during the first year of manufacture dates, the gas industry has asked DOE to move compliance to 2030, and the Supreme Court vacated the appeals court judgment that had upheld the standard and sent the case back for another look. None of these actions removes the October 6, 2026 compliance column from the CFR.
The 2023 rule is in force, with an October 6, 2026 compliance column for gas-fired storage water heaters at 95 percent thermal efficiency, gas-fired instantaneous water heaters and hot water supply boilers at 96 percent, and a tighter standby loss limit. Electric storage, electric instantaneous, oil-fired equipment and unfired storage tanks are unchanged.
DOE's May 5, 2026 enforcement discretion policy covers equipment manufactured on or after October 6, 2026 but before October 6, 2027, and only the specified gas-fired efficiency and certification obligations. The policy is not a final agency action and may be rescinded or modified.
Nothing in this article is legal advice. Manufacturers, distributors and owners should confirm their obligations with counsel.
Key Takeaways
In this article
What the regulation says today
The standards for commercial water heating equipment are codified at 10 CFR 431.110. Table 1 carries two sets of thermal efficiency values. For gas-fired storage water heaters and storage-type instantaneous water heaters, the minimum is 80 percent for equipment manufactured on or after October 9, 2015, and 95 percent for equipment manufactured on or after October 6, 2026. For gas-fired instantaneous water heaters and hot water supply boilers, the figures are 80 percent and 96 percent.
The standby loss limit for gas-fired storage units changes in the same column. The 2003-era formula is Q/800 + 110(Vr)^1/2 Btu/h, where Q is the rated input in Btu/h and Vr is the rated storage volume in gallons. The October 2026 column multiplies that result by 0.86.
Everything else in the table is unchanged across the two columns:
Electric storage water heaters: No thermal efficiency standard; standby loss limited to 0.30 + 27/Vm percent per hour, where Vm is measured storage volume in gallons.
Electric instantaneous water heaters: 80 percent thermal efficiency below 10 gallons, 77 percent at 10 gallons or more.
Oil-fired storage water heaters: 80 percent thermal efficiency; standby loss formula unchanged.
Oil-fired instantaneous water heaters and hot water supply boilers: 80 percent below 10 gallons, 78 percent at 10 gallons or more.
Two footnotes matter to storage design. Storage water heaters and hot water supply boilers over 140 gallons need not meet the standby loss limit if the tank surface is insulated to R-12.5 or more, no standing pilot is used, and gas or oil units have a flue damper or fan-assisted combustion.
Separately, section 431.110(b) requires unfired hot water storage tanks manufactured on or after October 29, 2003, to carry a minimum of R-12.5 insulation.
The rule also raised the uniform energy factor minimums for residential-duty commercial gas-fired storage water heaters, the class covering inputs above 75,000 and up to 105,000 Btu/h at 120 gallons or less. For the high draw pattern, the minimum moves from 0.6597 minus 0.0009 times Vr to 0.9297 minus 0.0009 times Vr. Oil-fired residential-duty units and electric instantaneous residential-duty units are unchanged.
Where the numbers came from
The amended standards were published in the Federal Register on October 6, 2023, at 88 FR 69686, with an effective date of December 5, 2023, and a compliance date three years out.
DOE projected 0.70 quads of primary energy saved over the 2026 to 2055 shipment period, about 5.6 percent below the no-new-standards case. The cumulative net present value of consumer benefits was estimated at $0.43 billion at a 7 percent discount rate and $1.43 billion at 3 percent. Cumulative emissions reductions over the same period were estimated at 38 million metric tons of CO2, 103 thousand tons of nitrogen oxides and 479 thousand tons of methane.
DOE stated in the rule and later documents that 95 and 96 percent thermal efficiency effectively require condensing technology. A non-condensing gas storage water heater vents through a conventional flue and has no condensate. A condensing unit recovers latent heat from the flue gas and produces an acidic condensate that must be handled.
The gas industry's position is that condensing is a different product with different installation requirements, not an efficiency level of the same product.
What DOE's enforcement policy does and does not do
On May 5, 2026, DOE's Office of the General Counsel published a Commercial Water Heater Enforcement Policy. As an exercise of enforcement discretion, DOE stated it will delay enforcement of the thermal efficiency standards for gas-fired storage water heaters, storage-type instantaneous water heaters, gas-fired instantaneous water heaters and hot water supply boilers manufactured on or after October 6, 2026 but before October 6, 2027. This is an enforcement policy, not a change to the compliance date in the regulation.
A clarifications document dated May 4, 2026 adds detail:
Civil penalties: The policy covers civil penalties for violations of the amended thermal efficiency standards in the listed gas-fired categories, and residential-duty commercial gas-fired storage water heaters.
Certification: It also covers the certification requirements at 10 CFR 429.12 for those categories.
Reason: DOE cites the pending Supreme Court petition and near-term market uncertainty.
Legal limits: The policy "may be rescinded or modified in the Department's complete discretion," "is not a final agency action," and "has no legally binding effect on persons or entities outside the federal government."
The policy does not mention the standby loss change. It does not address electric equipment, which was never subject to the amended thermal efficiency levels. It does not change the text of 10 CFR 431.110.
The policy does not speak to the obligations of distributors, installers or owners. Counsel, not a vendor article, is the right source for a specific project's exposure.
The petition and the court case
Two processes are running alongside the enforcement policy.
The first is a petition for rulemaking. The American Gas Association, the American Public Gas Association and the National Propane Gas Association filed it on February 19, 2026. DOE published a notification in the Federal Register on April 27, 2026 (91 FR 22477), seeking comment by May 27, 2026, on whether to grant it.
The petition asks DOE to extend the compliance dates for the commercial water heater standards and consumer furnace standards to January 1, 2030 at a minimum. The notice changes nothing; it asks whether DOE should open a rulemaking. As of this article's October 12, 2026 publish date, DOE has not published a decision.
The second is litigation. In American Gas Association v. Department of Energy, No. 25-879, the D.C. Circuit had upheld the 2023 furnace and commercial water heater standards.
On April 28, 2026, the Solicitor General filed a brief telling the Supreme Court that DOE now considers the December 2021 interpretive rule on which the standards relied, and the standards themselves, to be flawed, and that DOE is considering a new rulemaking.
On June 8, 2026, the Court granted the petition, vacated the judgment and remanded the case for further consideration in light of the government's position. Judgment issued July 10, 2026. The case is back before the D.C. Circuit. The vacatur removed the appeals court's ruling; it did not remove the regulation from the CFR.
How the standby loss arithmetic changes
The thermal efficiency change gets the attention, but the standby loss change touches storage design. Every calculation below uses the formulas in Table 1 of 10 CFR 431.110.
Gas-fired storage water heater: 100 gallons rated volume, 199,000 Btu/h input.
2003 column: 199,000 / 800 + 110 × (100)^1/2 = 248.75 + 1,100 = 1,348.75 Btu/h maximum standby loss.
October 2026 column: 0.86 × 1,348.75 = 1,159.9 Btu/h.
Difference over 24 hours: (1,348.75 − 1,159.9) × 24 = 4,532 Btu per day, about 1.3 kWh thermal per day per heater.
Electric storage water heater: 700 gallons measured volume, unchanged in both columns.
Standby loss limit: 0.30 + 27 / 700 = 0.3386 percent of stored heat above ambient per hour, or 8.13 percent per day.
Test conditions: Appendix B to Subpart G of Part 431 specifies mean tank temperature of 140 F plus or minus 5 F, ambient temperature of 75 F plus or minus 10 F, and k = 8.25 Btu per gallon-F. Stored heat above ambient is 700 × 8.25 × 65 = 375,375 Btu, so the limit is about 1,271 Btu/h, or 30,500 Btu per day.
Expressed as temperature: 30,500 Btu / (700 gal × 8.34 lb/gal × 1 Btu/lb-F) = 5.2 F per day.
For comparison, the TEHQ specification sheet for the 700-gallon Thermal Tank module lists heat loss of 2.4 F per 24 hours under free convection and a nominal insulation value of R-18, against the R-12.5 minimum the regulation sets for an unfired storage tank.
The TEHQ Thermal Tank module is an atmospheric unpressurized tank coupled to the potable system through a heat exchanger. It is not a water heater, and the water heater standby loss limit does not apply to it. The comparison is offered only to show the order of magnitude.
Standing loss, and why it matters more as storage volume grows, is covered in the best thermal energy tank specification guide. See also the TEHQ documentation library.
What this means for a replacement decision
An owner with a failing gas storage water heater in a commercial building faces four replacement paths.
Replace like for like with a condensing gas unit
A 95 percent thermal efficiency gas storage water heater meets the regulation as written. It needs a condensate drain and neutralization, and venting suited to a condensing appliance.
Fuel cost falls in proportion to the efficiency gain, and nothing about the electrical service changes. This path does not depend on how the litigation ends.
Install a non-condensing unit manufactured before October 6, 2026
Inventory manufactured before the compliance date was made under the 80 percent column. Units manufactured on or after October 6, 2026 but before October 6, 2027 sit inside DOE's enforcement discretion window, not a revised compliance date.
Both are a question for the distributor and counsel. The enforcement policy addresses DOE's civil penalty posture for the specified efficiency and certification obligations and nothing else, and it can be withdrawn.
Replace the heater with a heat pump water heater and storage
Electric commercial water heating equipment was not touched by the 2023 rule. A central heat pump water heater charging a storage volume sized for the peak period, with the heat pump sized for recovery rather than peak, removes the condensing question.
The project now touches the electrical service and demand charge. Storage lets the heat pump run longer at lower kW and shifts charging off the peak window.
The method is set out in the central heat pump water heater sizing and storage guide, and the retrofit sequence in how to electrify domestic hot water in existing multifamily buildings.
Keep a gas boiler and add unfired storage
A hot water supply boiler at 96 percent thermal efficiency paired with unfired storage tanks is the hybrid most engineers reach for in buildings where the electrical service cannot carry the load yet. The unfired tanks must meet the R-12.5 insulation minimum in 431.110(b).
The boiler is sized toward average load, and the tank carries the peak. The commercial hot water storage tank guide covers tank codes and sizing.
Why storage changes the calculus under any outcome
Whatever the D.C. Circuit or a new DOE rulemaking decides, the three structural facts behind the 2023 rule do not change.
A storage water heater loses heat continuously. Both columns of the table therefore regulate standby loss, and the over-140-gallon exemption is conditioned on R-12.5 insulation, no standing pilot, and a flue damper or fan-assisted combustion for gas or oil units.
Heating-source efficiency and storage volume are separate specifications. Storage volume determines whether the heating source can be sized small.
The only replacement path fully outside the gas rule is electric. Electric water heating in a commercial building is a demand charge problem before it is an energy problem.
For a worked illustration, assume a building replaces a 199,000 Btu/h gas storage water heater with a heat pump water heater at a COP of 2.5. For the same instantaneous output, the assumed electrical input is 199,000 / 3,412 / 2.5 = 23.3 kW.
Assume instead a 16-hour recovery period with storage carrying a three-hour peak. The same daily energy can be delivered at a fraction of that peak draw. The arithmetic for that trade is in the peak demand charges guide.
Check the assumed COP against the manufacturer's data at the building's entering water and ambient temperatures.
Timeline to watch
Each timeline entry is a public record and should be re-checked on the publish date and at each review.
Frequently Asked Questions
Did the DOE commercial water heater standard take effect on October 6, 2026?
The regulation at 10 CFR 431.110 lists October 6, 2026 as the manufacture date on or after which gas-fired storage water heaters must reach 95 percent thermal efficiency and gas-fired instantaneous water heaters and hot water supply boilers 96 percent. That text is in the CFR. DOE has separately published an enforcement discretion policy for the first year; it does not change the regulation.
Is the rule delayed?
Not in the regulation. DOE's May 5, 2026 policy says it will not seek civil penalties for the gas-fired thermal efficiency standards and certification requirements for units manufactured on or after October 6, 2026 but before October 6, 2027. The policy states it is not a final agency action and may be rescinded or modified. A petition to extend compliance to January 1, 2030 is pending, and DOE has not granted it as of this article's October 12, 2026 publish date.
Does the rule affect electric commercial water heaters?
No. The 2023 rule did not amend standards for electric storage or electric instantaneous water heaters. Electric storage units keep the standby loss limit of 0.30 + 27/Vm percent per hour, and electric instantaneous units keep 80 percent thermal efficiency under 10 gallons and 77 percent at 10 gallons or more.
What is the standby loss change for gas storage water heaters?
The maximum standby loss formula, Q/800 + 110(Vr)^1/2 Btu/h, is multiplied by 0.86 for units manufactured on or after October 6, 2026. For a 100-gallon, 199,000 Btu/h unit, that is 1,160 Btu/h instead of 1,349 Btu/h.
Do unfired storage tanks have to meet a standard?
Yes, a separate one that did not change. Unfired hot water storage tanks manufactured on or after October 29, 2003 must have at least R-12.5 insulation under 10 CFR 431.110(b). Storage water heaters over 140 gallons are exempt from the standby loss limit only if the tank is insulated to R-12.5 or more, has no standing pilot, and, for gas or oil units, has a flue damper or fan-assisted combustion.
What did the Supreme Court decide?
On June 8, 2026, in No. 25-879, the Court granted the petition, vacated the D.C. Circuit's judgment that had upheld the standards, and remanded the case in light of the Solicitor General's April 28, 2026 brief. The case is back at the D.C. Circuit. The order did not strike the regulation.
Should a replacement be specified to the new standard now?
That is a question for the engineer of record and counsel. The regulation as written requires 95 or 96 percent thermal efficiency for gas-fired units manufactured on or after October 6, 2026. Specifying to that level, or specifying an electric heat pump system with storage that is outside the gas rule, are the two paths that hold under any outcome of the petition and litigation.
How does this relate to the 2029 residential water heater rule?
It does not, except that both came out of the same 2023 round of DOE rulemaking and both are contested. The residential rule, with its May 6, 2029 compliance date, is covered in the DOE residential water heater standards 2029 article.
The bottom line
The commercial water heater standard is in the CFR with an October 6, 2026 compliance column: 95 percent thermal efficiency for gas-fired storage, 96 percent for gas-fired instantaneous and hot water supply boilers, and a standby loss limit 14 percent tighter.
DOE's enforcement discretion policy says it will not seek civil penalties for the specified gas-fired efficiency and certification obligations for equipment manufactured on or after October 6, 2026 but before October 6, 2027. It does not change the regulation, is not a final agency action, and may be rescinded or modified. A petition to move compliance to 2030 is pending, and the court case is back at the D.C. Circuit.
None of that changes the engineering. A condensing gas unit meets the rule as written. An electric heat pump system with properly sized storage is outside the gas rule and converts the problem into one of electrical capacity and demand charges, which storage is built to address.
Re-check every regulatory statement in this article on the day it is used, and confirm the specific project's obligations with counsel.
