The new water heater rule requires heat pump technology by 2029
A new Department of Energy rule sets an efficiency level for electric storage water heaters bigger than 35 gallons that only heat pump technology can reach, and manufacturers must meet it starting May 6, 2029. A heat pump water heater moves existing heat from the surrounding air into the tank instead of generating heat directly from electricity, the way a standard electric resistance water heater does. The Department of Energy published this final rule on May 6, 2024, giving manufacturers exactly 5 years to comply. A. O. Smith, a water heater manufacturer, also states on its own site that residential compliance is required by May 2029. Smaller tanks, 20 to 35 gallons, and much larger tanks, over 55 gallons, keep a path that does not need a heat pump, so the new water heater rule lands on the size range in between.
Why only heat pump technology can meet the new standard
The rule measures efficiency with a uniform energy factor, a single number describing how much hot water a unit delivers for the energy it uses. A water heater bigger than 35 gallons and up to 55 gallons now has to hit a factor of 2.3 or higher. A flat electric resistance water heater cannot pass a factor of 1, because it only converts electricity straight into heat. A heat pump moves existing heat instead of generating it, so it can report a factor well above 1. The California Energy Commission told the Department of Energy in comments on the rule that even the least efficient heat pump water heaters already sold carry a factor of 2.8 or higher. That gap is why electric storage water heaters bigger than 35 gallons will effectively have to be heat pump models once 2029 arrives.
Show the numbers
| Ordinary electric resistance heating | 1 |
| New minimum required above 35 gallons | 2.3 |
| Least efficient heat pump already on the market | 2.8 |
The 3 size classes the rule creates
The final rule sorts electric storage water heaters into 3 size classes. Tanks of 20 to 35 gallons form a small class that can still use plain electric resistance heating. Tanks bigger than 35 gallons and up to 55 gallons must hit the 2.3 factor described above. Tanks bigger than 55 gallons and up to 120 gallons form a third class that must meet an even higher factor, not given as a single number in the rule. The current regulation, 10 CFR 430.32, confirms the 20 to 35 gallon boundary in the same words twice, once for the standard already in force and once for the standard that takes over in 2029.
The middle class is the one that must use heat pump technology to meet its efficiency requirement.
Show the numbers
| Small class | 20 to 35 gallons, resistance heating still allowed |
| Heat pump required class | 35 to 55 gallons, must reach a uniform energy factor of 2.3 |
| Largest class | 55 to 120 gallons, an even higher factor required |
What stays true for buyers right now
Nothing changes for anyone buying a water heater today. Compliance is not required until May 6, 2029, and one 2026 explainer aimed at installers describes the rule as still facing ongoing legal challenges and postponements, so 2029 is the current legal deadline, not a settled fact. Only 1% of United States households used a heat pump water heater as of 2023, the year the rule was proposed, according to Grist reporting from that year. When the rule was still a proposal, Susan Weinstock, chief executive officer of the Consumer Federation of America, said this.
Although long overdue, the efficiency standards proposed by DOE will deliver significant savings for consumers over the life of the water heater.
Susan Weinstock, Chief Executive Officer, Consumer Federation of America. Source 5.
The impact the rule itself projects
The Department of Energy states in its own final rule that the standard will avoid 332 million metric tons of carbon dioxide over 30 years. A separate 2025 repeal of a different Department of Energy rule, covering gas fired tankless water heaters, does not affect this electric storage rule, a distinct product category under a distinct legal action.