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Powering Electric Water Heater w/Generator

Post in 'DIY and General non-hearth advice' started by thinkxingu, Oct 4, 2010.

  1. thinkxingu

    thinkxingu Minister of Fire

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    OK, so I recently installed an interlock kit on my main panel (no room for transfer switch/wanted access to all circuits) and I'm wondering what the 411 is on running an electric water heater.

    1. I've got a 5500 watt genny; am I right in assuming that, as long as I'm not running many other things, that it'd be ok to run my water heater?
    2. Also, does the h20 heater always pull 4500 watts or only upon turn-on?
    3. Would it be best to keep the h20 heater off and only run at night/when needed or would it be best to run continuousally to maintain the temp?

    Thanks,

    S

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  2. vvvv

    vvvv New Member

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    2-yes
    3-if u can coordinate ur hot water needs with the heater u can save some. heater only experiences standby loss when water is hot
    1-goes to theory, but i run a mini oven & exhaust fan on same plug & when the oven heats, the fan slows down- i can hear it
  3. thinkxingu

    thinkxingu Minister of Fire

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    ~*~vvv~*~:
    What do you mean coordinate hot water needs with heater? Do you mean to only run it when I'm using hot water?

    S
  4. nate379

    nate379 Guest

    You would have to run that just on it's own, as you would not have enough generator for anything else really. Maybe a couple lights, but that's it.

    Run the heater enough for whoever to take a quick shower and then shut it off.
  5. thinkxingu

    thinkxingu Minister of Fire

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    It sounds like I should run it overnight to re-heat whatever was used. I have a 50-gallon, and we had warm water the last time we lost power for two days. I was just thinking that it would take less power to maintain water at temp than to re-heat after cooling down, but it sounds like it's all-or-nothing as far as power draw. Of course, it would take less time to re-heat a small amount of new, cool water than to re-heat both cooled down water and new, cool water.

    S
  6. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    Yep it is all or nothing. I have a Blue Line power monitor. The house usually is running at half a Kwh or so during the day and anytime that water heater kicks the meter goes straight to over five Kwh until it shuts off. You would knock a five thousand watt generator to its knees.
  7. thinkxingu

    thinkxingu Minister of Fire

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    Bart, that would only be if I was running other things. At night, what's the draw--a couple watts for displays and the fridge kicking on once or twice?

    S
  8. nate379

    nate379 Guest

    All depends on the fridge. Mine seems like it's almost always running. One of them fancy $2300 digital display opens your beer for you units.
  9. Highbeam

    Highbeam Minister of Fire

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    When using my genset with interlock I shut off the water heater and hot tub. The fridge and freezer cycle and are on different "legs" of the panel so all is well. The water heater certainly can be powered by a genset through an adequately sized generator circuit that matches or exceeds the circuit rating of the water heater circuit but you need enough balls from your genset. I would be okay running a 4500 watt load from a 5500 watt genset since the water heater is a resistive 240 volt load with no big surge at startup. Your 5500 is rated continuous at 5500 right? None of this 5500 watt surge rating business? Be sure that other devices with sensitive electronics are not hooked up just in case you get a voltage dip.
  10. thinkxingu

    thinkxingu Minister of Fire

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    Highbeam,
    The generator's rated at 5550 running watts and 8250 start-up. If running the water heater, only the fridge and displays, etc. would be running (at night/morning = no lights, tv, computer, etc.). In talking to the local inspector, it sounds like it's all about managing usage when using a smaller generator.

    NOW: what's the largest generator I could run with the 30 amp box, breaker, and 10 awg wire I used?

    S
  11. ROBERT F

    ROBERT F Minister of Fire

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    If the water heater was drawing on both elements at the same time, and the fridge's compressor went to start up, you would be short on power for just long enough to do damage to the fridge over time. might not happen the first time, but repeat a few times and ????
  12. thinkxingu

    thinkxingu Minister of Fire

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    Two things:

    1. I've read that water heaters only use one element at a time, which is regulated by the thermostats.
    2. My heater says 3,800 is the draw for each element.

    S
  13. maverick06

    maverick06 Minister of Fire

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    the water heater wont have a *peak* draw like a ac motor has, just a heavy load.

    If you just heat up the tank overnight it will be plenty good. i have my home water heater on the "off peak" meter, so it is only energized from about 6pm until 6 am. But if you go to take a shower at 5pm, the water is still nice and hot since it hasnt been used much durring the day.

    I looked into this, and told my wife that if power is out, so is the hot water... my generator wont run that, the AC or the stove... everything else is fair game.
  14. vvvv

    vvvv New Member

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    turn it on 1 hr be4 using hot water, then turn it off be4 u using hot water. drain the tank from usage & leave it full of cold water until next episode= minimal standby heatloss
  15. vvvv

    vvvv New Member

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    3800 X2 = 7600 for cold water startup, i think
  16. Highbeam

    Highbeam Minister of Fire

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    3800 times two elements would be 7600 watts at 240 volts would be 31.66 amps. All of the water heater circuits that I have seen are fed by 30 amp breakers. How can you know if both elements fire at once? It would seem as though they can't without blowing the breaker.

    If both elements are on and you want to run them from a genset then you would need at least 7600 watts of honest generator capacity and you would need more than the 30 amp generator circuit can provide. As such, unless you can disable or be certain that only one element fires at a time, you can't run that water heater with the 30 amp generator circuit.

    Given that your water heater circuit has a 30 amp breaker and that your generator circuit has a 30 amp breaker AND if you can acquire a genset that can make the full 7600 continuous watts I would try it. I would shut off all other circuits including the fridge during this loading. Your fridge will stay cold overnight if you don't open the door.
  17. Highbeam

    Highbeam Minister of Fire

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    If having hot water at all times is this important to you, perhaps it is time to switch to a gas water heater?

    I've just decided that we won't have hot water during an outage and if I need it really bad then I can go out into the RV and fire up the 6 gallon LPG water heater, furnace, and take a shower out there. It is good to have a second home that needs no utility power.
  18. Cowboy Billy

    Cowboy Billy Minister of Fire

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    Highbeam

    Thats what we are planing on doing at the farm for a outside shower in the summer. My brother found a tank less propane hot water heater for $150 on epay. But I haven't got the wood cut to build it yet.

    Billy
  19. thinkxingu

    thinkxingu Minister of Fire

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    As mentioned, it's not a huge deal since the water stays warm for a few days without power anyway. I was just thinking that since it's all hooked up, why not keep the h20 hot?

    S
  20. vvvv

    vvvv New Member

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    critical q= caN THE WHEATER SLOW DOWN THE GENERATOR? i know a motor can but dunno if electric elements can.......& i'm betting they cant.................ya , overloaded my gen with a circ saw but it didnt work under cutting load== bla bla===it will work, no prob..................any bets? 1-1 odds
  21. begreen

    begreen Mooderator Staff Member

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    No, both elements do not come on at once. The upper will come on if the tank is cold. Lower if it is warm.
  22. thinkxingu

    thinkxingu Minister of Fire

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    Right, so 3800 watts on a 5500 watt generator should be no problem. As for gas, that's out: I have it at the street, but I'd never recoup the costs associated with changing heating systems. The question is still: what would be the best time to run the h20 heater? At night, after using it, just leave it on because keeping it warm doesn't take as much energy as heating it up?

    S
  23. vvvv

    vvvv New Member

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    dunno where the 4500w came from? last i worked on heater there were 2 elements & each had its own thermostat, i assume that when full of cold water both elements will burn because each thermostat will be calling for heat
  24. vvvv

    vvvv New Member

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    standby heatloss from water heater can only happen when full of hot water. if tank is cold it loses no heat & heating cold tank uses no more energy than constantly reheating warm water. I still think heater will work if both elements fire at the same time but i aint sure. member Cozyheat is an electrical engineer ithink
  25. kabbott

    kabbott Member

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    I am pretty sure that when the top thermostat comes on it cuts the bottom element off. That lets the top element heat up top half of tank
    so you get your hot water back faster. I 'think' my top element is 4500 watt but my bottom element is only 1500???

    Kris

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