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Thread: Two elements vs. one element

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    Default Two elements vs. one element

    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.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    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.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Moderator & Master Plumber hj's Avatar
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    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.

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    Quote Originally Posted by hj View Post
    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.
    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.

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    Moderator & Master Plumber hj's Avatar
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    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.

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    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?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    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 by jadnashua; 02-28-2010 at 01:33 PM.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    My understanding is that only one element at a time is operating, therefore a 30 amp circuit is adequate. Is this correct?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Normally, but you asked about whether both could be on, and there are some that can do that.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Moderator & Master Plumber hj's Avatar
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    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.

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    DIY Member Lightwave's Avatar
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    Quote Originally Posted by jadnashua View Post
    Also, the larger draw could cause the lights to flicker when the thing turns on. That's a large load to switch.
    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.

    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.
    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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