240V vs 208V Water Heater Element: What Changes

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Quick answer from a licensed plumber: A 240-volt element on 208 volts still heats, at about 75% of its rating: Rheem says a 4500-watt element delivers 3380 watts and a 5500-watt element about 4130. Rheem’s residential electric heaters are dual rated for both voltages, so if your rating plate says 240 V, buy the 240-volt element. Buy a 208-volt or 120-volt element only when the rating plate lists that voltage. Never go the other way: Rheem says an element given more than its design voltage “will burn out.”

Rating plate says 240 V / 4500 W? It is the right part on 208-volt power too, with lower output. See the Rheem SP10869MM on Amazon

What a 240-Volt Element Puts Out on 208 Volts

Rheem’s bulletin on residential electric heaters says they “are dual rated for 240 and 208 Volts AC single phase operation,” and it prints what each common element delivers on each voltage:

Recovery in that table is at a 90°F temperature rise. The Rheem element listings print the same 208-volt numbers: the SP10869MM gives “wattage at 208V (W): 3380” and the SP10869PH gives 4130.

Why the Output Drops by a Quarter

An element is a fixed resistance, so its output falls with the square of the voltage. Rheem shows the math: 208 squared is 43,264, 240 squared is 57,600, so the element runs at 75.111% of its rating, and on 208 volts a 240-volt, 5500-watt element “will deliver only 4131 watts of heat energy into the water.” Rheem’s conclusion: “When less than design voltage is supplied to the heating element, the element will still heat, but at less than the design value,” and “The heater takes longer to recover its’ contents.”

So Which Element Do You Buy?

• Your rating plate lists 240 V. Buy the 240-volt element at the plate’s wattage, even if the building supplies 208 volts. That is the dual rating Rheem describes, and A. O. Smith says replacement elements must “be the same voltage and … no greater wattage than listed on the model rating plate.”
• Your rating plate lists 208 V. Rheem’s dual rating “does not include … units specifically configured for 208 volt AC operation.” Buy a 208-volt element. Bradford White’s parts list, for example, carries separate 208-volt and 240-volt part numbers at the same wattage.
• Your rating plate lists 120 V. That is usually a small point-of-use heater, which Rheem also excludes from the dual rating (A. O. Smith’s element availability sheet also lists 120-volt inputs for some 30- to 50-gallon models). Buy a 120-volt element.

Rheem’s down-rating bulletin ends with a caution: “Rheem Manufacturing does not recommend the down-rating of electrical heating elements.” Its separate dual-voltage bulletin is the one that covers 208-volt operation, and it sends you to “the rating label for the specified voltage and wattage rating.” And A. O. Smith’s Voltex heat pump water heater is a different case entirely: its manual says to provide 240 VAC and “DO NOT use 208 VAC.”

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How Many Amps, and What Circuit

Rheem’s tables are written for elements rated at each voltage:

Rheem’s bulletin opens with “Please check all local electrical codes before installing or changing wiring on electric water heaters.” Circuit changes are work for a licensed electrician.

120-Volt Elements Are a Different Part

The 120-volt elements we checked are shorter and lower powered. Rheem’s SP10874GH is 120 V / 2000 W with a 7.65-inch flange-to-tip length, against about 13.5 inches for its 240-volt elements, per the listings. Camco’s listing says its 2000 W / 120 V element needs a “Minimum Tank Diameter: 9 inch.” Match the voltage and wattage on the rating plate, as A. O. Smith’s point-of-use manual requires.

What to Buy

Matched to the rating plate:

• Plate says 240 V / 4500 W (on 240 or 208 V power): Rheem SP10869MM 240 V / 4500 W, sold by Amazon.
• Plate says 240 V / 5500 W: Rheem SP10869PH 240 V / 5500 W, sold by Amazon.
• Plate says 120 V / 2000 W: Rheem SP10874GH 120 V / 2000 W or Camco 2000 W / 120 V, both sold by Amazon.

We did not check any 208-volt-rated elements on Amazon for this page; for a heater configured for 208 volts, order the element by model number from the maker’s parts channel. The wattage choice itself is covered in our 4500 vs 5500 watt element guide.

Parts You’ll Also Need

Refill the tank before you restore power; A. O. Smith says power to a tank that is not completely full “will cause the upper heating element to burn out.” For the swap:

• Camco 09883 element wrench, sold by Amazon; its listing says it fits the 1-1/2 in. hex on residential screw-in elements.
• Klein Tools NCVT3P non-contact voltage tester, sold by Amazon, to confirm the power is off as A. O. Smith’s steps require.

When to Call a Licensed Pro

• You do not know whether the building supplies 208 or 240 volts. A licensed electrician can tell you.
• The rating plate is missing or unreadable.
• You want a faster-recovering heater on 208-volt power. That is a heater and circuit decision, not an element swap. Electric tankless units lose output on 208 volts too; see our tankless water heater guide.

FAQ

Can I use a 240V water heater element on 208V?

Yes, when the heater’s rating plate lists 240 volts. Rheem says its residential electric heaters are dual rated for 240 and 208 volts, and a 240-volt element on 208 volts still heats, at about 75% of its rating.

How many watts does a 4500 watt element produce on 208 volts?

About 3380 watts, per Rheem’s dual-voltage table and its SP10869MM listing. A 5500-watt element produces about 4130 watts.

Should I buy a 208V element for a 208V building?

Only if the heater’s rating plate lists 208 volts. Rheem says its dual rating does not cover units specifically configured for 208 volts, and A. O. Smith says replacement elements must match the rating plate voltage.

What happens if I put a 120V element in a 240V heater?

Rheem says that when more than the design voltage is supplied to an element, it will burn out.

Can a heat pump water heater run on 208 volts?

Not A. O. Smith’s Voltex. Its manual says to supply 240 VAC and not to use 208 VAC.

Why Trust Plumbing Picks

Plumbing Picks is written by a licensed Georgia journeyman plumber. Every part number, size, rating and fit on this page comes from the manufacturer pages and documents listed below, which we opened and read, or, where the page says so, from an Amazon listing; none of it comes from hands-on testing. Each linked product was shipped or sold by Amazon, new and in stock, when we checked on September 24, 2026. Where a link goes to Amazon we may earn a commission at no extra cost to you. Nobody pays to be included here. More on who writes this and how we pick.

Sources

• Rheem Technical Service Bulletin 1317: Dual Voltage Rating on Residential Electric Water Heaters
• Rheem Technical Service Bulletin 1306: Statement of Down-Rating Electrical Heating Elements
• Rheem Technical Service Bulletin 1305: Heating Element Properties (voltage, amps, ohms, recovery, circuit breaker)
• A. O. Smith: residential electric 120-volt point-of-use manual 185834-000
• A. O. Smith: Voltex Hybrid Electric Heat Pump Water Heater manual 318257-002
• A. O. Smith: Residential Electric Water Heater Installation Instructions and Use & Care Guide (March 2021)
• A. O. Smith: Residential Electric Element Availability Sheet AOSTD63000 (recovery table)
• Bradford White: Residential Electric Replacement Parts List 238-51382-00AA (July 2025)

Bottom Line

Buy the voltage on the rating plate. A 240-volt element on 208 volts runs at about 75%: 4500 becomes 3380 watts and 5500 becomes about 4130, with slower recovery. Rheem does not recommend down-rating, heat pump models may not allow 208 volts at all, and any wiring change goes to a licensed electrician.