Last reviewed: September 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards
Replacing a water heater comes down to three decisions: fuel, capacity and whether to move to a heat pump water heater. Federal minimum efficiency is set by formula, not by a single number, and it changes for units manufactured on or after May 6, 2029.
One rule that does not apply: the tougher standard for gas tankless water heaters. Congress disapproved it, and the Department of Energy formally withdrew the rule on May 20, 2025.
How federal efficiency rules work here
Water heaters are rated by Uniform Energy Factor, and the minimum is a formula rather than a fixed figure. It varies by product class, storage volume and draw pattern, which is why any page quoting “the minimum UEF” has quietly fixed all three.
Under 10 CFR 430.32(d), a gas-fired storage water heater between 20 and 55 gallons on a medium draw pattern must reach a UEF of 0.6483 minus 0.0017 times the rated volume. A 50 gallon unit therefore needs about 0.563. The equivalent electric storage class needs 0.9307 minus 0.0002 times volume, about 0.921.
| Class (medium draw) | Formula, before May 6, 2029 | At 50 gallons |
|---|---|---|
| Gas-fired storage, 20 to 55 gal | 0.6483 − (0.0017 × volume) | 0.563 |
| Electric storage, 20 to 55 gal | 0.9307 − (0.0002 × volume) | 0.921 |
| Oil-fired storage, up to 50 gal | 0.6078 − (0.0016 × volume) | 0.528 |
| Electric storage, over 55 gal | 2.1171 − (0.0011 × volume) | 2.029 at 80 gal |
That last row is the important one. A UEF above 1.0 means the appliance delivers more energy than it consumes, which resistance elements cannot do. The large electric classes are effectively heat pump water heaters by regulation.
What changes in 2029
A second table in the same section applies to units manufactured on or after May 6, 2029, and it is based on effective storage volume rather than rated volume. It also adds classes below 20 gallons and above 100 gallons that the current table does not cover.
This affects manufacture date, not your installation. A compliant heater built before that date remains legal to sell and install afterwards, the same principle that governs SEER2 minimums for cooling equipment.
DOE published amended standards for consumer gas-fired instantaneous water heaters on December 26, 2024 (89 FR 105188), with an effective date of March 11, 2025. The effective date was delayed twice, and on May 20, 2025 DOE withdrew the rule entirely (90 FR 21390), stating it was acting “Pursuant to the Congressional Review Act” to withdraw “a disapproved final rule”. Gas tankless water heaters are therefore still governed by the earlier standard, and any page describing a new tankless minimum is out of date.
Sizing: first hour rating, not gallons
Tank size is the number everyone quotes and the wrong one to buy on. The useful figure is the first hour rating, how much hot water the unit can deliver in the busiest hour, which combines tank volume with recovery rate.
- Work out your peak hour, usually a morning: showers, a dishwasher, a laundry load.
- Add the demand in gallons for that hour.
- Match the first hour rating to that figure, not to the tank size of the old unit.
- For tankless, the equivalent is flow in gallons per minute at your incoming water temperature. Cold inlet water cuts deliverable flow, so a unit sized for a southern climate underperforms in a northern one.
A heat pump water heater has a further constraint: it needs air volume and clearance around it, and it cools and dehumidifies the space it sits in.
Fuel cost, honestly
Water heating cost follows the same fuel prices as space heating. At 2025/26 season averages, natural gas cost about $15.05 per million Btu of fuel against about $52.10 for electricity.
That gap is why gas has been cheaper to run, and why a heat pump water heater changes the comparison: by moving heat rather than making it, it uses a fraction of the electricity a resistance element does. Our page on what heat costs by fuel sets out the arithmetic and the assumptions behind it.
What the market is doing
Shipments are falling on both fuels. Through July 2026, gas storage water heater shipments were 2,487,389 units, down 2.5% on 2025, and electric storage was 2,877,192, down 5.2%.
Electric is also down 5.5% against the same period of 2024, so this is a two-year decline rather than one soft season. More in our water heater shipments and standards report.
Frequently asked questions
What size water heater do I need?
Match the first hour rating to your peak hour demand rather than matching the old tank’s gallon size. Add up the hot water used in your busiest hour, usually a morning, and buy to that figure. For tankless, size on gallons per minute at your winter incoming water temperature.
Are there new federal water heater standards?
Yes for storage water heaters: a new table of minimum Uniform Energy Factors applies to units manufactured on or after May 6, 2029, under 10 CFR 430.32(d). For gas tankless there is no new standard: DOE’s December 2024 rule was disapproved by Congress and withdrawn on May 20, 2025.
Is a heat pump water heater worth it?
It uses far less electricity than a resistance element because it moves heat rather than generating it, which is why federal minimums for the larger electric classes require a UEF above 1.0, a level only a heat pump can reach. It needs clearance and air volume, and it cools the space it occupies. No federal source publishes installed costs, so we do not quote a payback.
Gas or electric water heater?
On fuel price alone gas has been cheaper: about $15.05 per million Btu against $52.10 for electricity at 2025/26 season averages. A heat pump water heater narrows or closes that gap by using a fraction of the electricity. Venting, existing connections and local prices decide the rest.
Methodology and limitations
Efficiency requirements are quoted from 10 CFR 430.32(d). Rulemaking history is from Federal Register documents 89 FR 105188, 90 FR 9951, 90 FR 13054 and 90 FR 21390. Shipments are AHRI’s July 2026 release. Fuel prices are EIA season averages as documented on our fuel cost page.
- Worked UEF examples assume a medium draw pattern; other draw patterns have different formulas.
- Standards apply to manufacture date, not installation date.
- We publish no installed prices or payback periods, because no federal series measures them.
Sources
- Code of Federal Regulations, 10 CFR 430.32(d), water heater energy conservation standards.
- US Department of Energy, “Energy Conservation Standards for Consumer Gas-Fired Instantaneous Water Heaters”, final rule 89 FR 105188 (December 26, 2024) and final rule; withdrawal, 90 FR 21390 (May 20, 2025).
- Air-Conditioning, Heating, and Refrigeration Institute, July 2026 shipment release.
The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.
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