Two elements vs. one element

Discussion in 'Water Heater Forum, Tanks' started by comfun1, Feb 27, 2010.

  1. comfun1

    comfun1 New Member

    Messages:
    12
    Location:
    S.E. Kansas
    I'm building a new house and am wondering, is it better to use a hot water with two elements rated at 4500w or a water heater with a single element rated at 5500w? The catalog claims the 5500w has a 20% quicker recovery rate.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,947
    Location:
    New England
    It's quicker because it is 20% bigger, not because it is one element verses two. With two elements, they are normally setup to operate with one or the other, not both. The hot water comes off of the top of the WH and the dip tube directs the incoming cold water towards the bottom of the tank. When you get close to running out of hot, the only element that normally is running is the one at the top which is trying to keep the water going out the pipe as hot as it can get it; otherwise, the bottom one kicks on once the top reaches the set point. So, with only one at the bottom, you might recover quicker, but the last of the water coming out might just end up getting colder and colder without that extra kick of the upper element. I'm told that you can get some where it can operate both elements at the same time, which would be larger than the single element one. Either might require rewiring and a new breaker, as the current draw is larger.
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,534
    Location:
    Cave Creek, Arizona
    You can get two element heaters with 5500 watt elements. With 2 elements, you have a "backup" when the lower one burns out, which will keep some hot water in the tank until it is repaired. With one element, when it burns out you have NO hot water until it is fixed. One element heaters are usually a lower level model than those with two elements. In fact, Bradford White one element heaters often only have a one year warranty.
  4. comfun1

    comfun1 New Member

    Messages:
    12
    Location:
    S.E. Kansas
    Do you know what brand has two element/5500 watts? All the duals I have found are 4500. I did find a hybrid but I don't see how it would help me. If I put it in the garage it's going to take the heat out of the air and in the winter that might be enough to freeze my pipes.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,534
    Location:
    Cave Creek, Arizona
    Every brand can be ordered with them. AO Smith ProMax can be ordered with 4500, 5500, or 6000 watt elements. Some 9, 10, and 12 year warranty heaters come with 5500 watt elements so you actually get some benefits from the extra cost.
  6. comfun1

    comfun1 New Member

    Messages:
    12
    Location:
    S.E. Kansas
    So, other than a quicker recovery is there an advantage or disadvantage of 4500/5500 watt? It seems like if I can get a 5500 watt, why would I want a 4500 watt. There would be no more energy consumed with the 5500 watt since it would be on a shorter time than the 4500 watt. I'm thinking a 5500 watt dual element with all the insulation I can get would be the best. Perhaps a jacket as well. Does this seem right? Why aren't they all made with 5500 watt elements to start with?
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,947
    Location:
    New England
    A dual 5500W element WH would likely need a 60A circuit with the associated fairly large supply wires. One dual-element (only one on at a time) would use a 30A circuit. So, there's the cost of the wire, which could be substantial. Also, the larger draw could cause the lights to flicker when the thing turns on. That's a large load to switch.

    Say you have a heat pump with auxilliary emergency heat, an electric dryer, and stove. If they all were on at the same time, you could even pop your main breaker, depending on what your main supply service is.
    Last edited: Feb 28, 2010
  8. comfun1

    comfun1 New Member

    Messages:
    12
    Location:
    S.E. Kansas
    My understanding is that only one element at a time is operating, therefore a 30 amp circuit is adequate. Is this correct?
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,947
    Location:
    New England
    Normally, but you asked about whether both could be on, and there are some that can do that.
  10. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,534
    Location:
    Cave Creek, Arizona
    NO reidential water heaters are wired for simultaneous operation and usually, only 3 phase commercial ones are simultaneous because of the reduced load on the wiring. IF I rewire a residential heater for simultaneous operation in a business, I either convert it to 3 phase, or use two separate power feeds.
  11. Lightwave

    Lightwave New Member

    Messages:
    98
    Location:
    Vancouver, BC
    That depends to a huge extent on your breaker panel and service wiring. A 10KW heating load doesn't dip the lights here, but this is with a 200A service.

    Calculations would be required to verify that the service can handle the load. The NEC has a how-to for this.
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