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Community and Q&A

Water Heater 120 v 240

alan72 | Posted in General Questions on

New construction 
Climate zone 5
Large solar system with battery backup
No gas supply

We are specifying our hot water heater and are looking at the Rheem Proterra Hydrid water heater.

What considerations are there to choose between a 120v and 240v for the electric water heater?  Both are available.

(I’m not sure how 120v or 240v affects efficiency, back to back showers, anything else?)



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  1. user-2310254 | | #1


    The 15 amp version is also 240 volt, but the draw from the heating element is lower.

    1. alan72 | | #2

      Thanks Steve, so does it matter which one we choose (from an electrical standpoint)?

      I think the 240v model needs a 30amp breaker.

      Part of me thinks that from a hot water on demand standpoint, we would choose the 240v model.

      The choice for the 120v would keep us with hot water in the event of a power outage and we are running on Powerwall power - (lower amp) - does that make sense?


      1. this_page_left_blank | | #3

        There is no 120V version of Pro Terra. There's 240V 30A and 240V 15A. The 30A version can also have a leak guard.

  2. alan72 | | #4

    I am making an error here - I assumed the 15amp version is 120v and the 30 amp is 240v.

    Any reason to choose the 30amp version over the 15 amp or vice versa?

  3. Expert Member
    BILL WICHERS | | #5

    According to the datasheet here:

    The 15A version has a 2,250 watt heating element while the 30A version has a 4,500 watt heating element. The compressor capacity for the heat pump mode is the same for both. I see only 240 volt options, no 120 volt model. If you have a link to the datasheet for a 120 volt model I can take a look at it for you.

    The bigger heating element would give more power in the electric mode, which would likely mean quicker refresh rates for periods of high use like long showers.

    What matters in terms of energy is the wattage, not the voltage. If, for example, you have two heaters of 1,000 watts each, but one is a 120v heater and the other a 240v heater, you'll be getting exactly the same amount of heat out of each one, but the 240 volt heater will use half the amps as the 120 volt version. Efficiency in the wiring tends to be a bit higher for 240 volt versions of things too since losses are a function of current (amperes), not wattage. This is why power lines use very high voltages for power transmission.

    I would normally prefer a 240 volt unit when possible, especially for a heavy load like a water heater. In your case, assuming there is only a 240 volt option, you're probably going to be happier with the 30A version, and it won't cost you any extra to run unless you actually need it, since the heat pump part is the same capacity for both versions and that's the part that will likely run the most over time.


  4. user-2310254 | | #6


    Don’t feel bad. I made the same assumption when Rheem announced the 15 amp HPWH a couple of years ago. I think that model is intended for situations where an owner has limits on his/her electrical service. I had to put in a sub panel and a new circuit for my 80 gallon, 30 amp unit.

  5. bigred | | #7

    I installed the Rheem 50 gallon unit almost exactly 2 years ago now. Its a really nice unit and very efficient. I was replacing a conventional electric unit so already had a 30 amp circuit already there. I think the biggest difference is how much hot water the backup resistance heaters can make. The lower rated unit will be much slower to recover from high usage. Now it's just my wife and I, but we have never run out of Hot water. If I had a teenager at home, that might be a different story. I normally run it on hybrid mode so it will use the backup elements if it senses very high water usage, such as if we have company and multiple showers. It also doesn't hurt we are in Texas and the garage can get pretty warm in the summer and seldom gets below about 55 in the winter (all walls, garage door and ceiling are well insulated.

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