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Thread: Going To Toss The Sidearm And Install An Electric Tank

  1. #1
    DIY Member drizler's Avatar
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    Default Going To Toss The Sidearm And Install An Electric Tank

    I don't use my boiler for anything but heating hot water anyways and the sidearm tank just died. While expensive here in NY State it seems to make more sense to just put in an electric tank and install it upstairs where it is warm rather than the cold basement.

    How many kilowatts does a family of 3 usually use with a shower a day each and no one being a shower hog? Nobody showers one after the other either.

    The tank we currently have is a 30 gallon sidearm so I would assume a 40 gallon electric would replace it well enough. We have a 55 gallon whirlpool tub that rarely gets used but the sidearm 30 barely filled it.

    I plan on just using the Peerless boiler during the winter as a backup and draining it for the majority of the year and do all my heat as I do now with the pellet stove.
    Is there anything I am missing here?

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    A boiler assisted tank can heat a lot more water than an electric. The recovery rate is higher as well, so a 40-gallon electric may not (likely won't) fill the tub. Once hot, it doesn't take all that much to keep it hot in an electric tank. A Kw=3412BTU. One BTU can raise one pound of water one degree. So, depending on how cold the water coming in is, and how hot you make it, and how much you use, you can figure it out. A gallon of water weighs about 8# (less, but that would give you some room for standby losses).

    So, to raise 40-gallons of water from say 40-degrees to 120-degrees (about the minimum you want) means:
    40*8 or 320# of water, *80 degrees, or 25600BTU /3412 = about 7.5Kwhr.

    Then, add in any other hot uses during the day, and you can figure out approximately how much energy it will take; then, multiply by the local rates. Sometimes, it is a tiered rate, and the more you use, the higher the cost/Kw, so it might bump you up to a higher rate.
    Last edited by jadnashua; 02-24-2011 at 06:05 PM.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Member drizler's Avatar
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    Thanks for the explaination. I guess a 40 will fill the bill fine. One last thing. Any specific wiring schematics out there for one of these. I have replaced a few in my day but they were all many years between and already set up. Off hand I am assuming a 12/2 romex straight to it's own circuit at the box with no other special considerations. I am going to put this in an drain pan like no one ever does for that eventual day it leaks. Any big consideration on models / makes besides the warranty? I don't plan on getting anything magnificant as changing out an annode is no big deal to me every 5 years or so. Neither is draining and flushing.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    Depends on the model you purchase, but I doubt 12g would cut it. Most spec either a 30A or 40A circuit breaker (full-sized, 240vac), and you have to abide by the rules based on the load and the installation instructions of the one you get. Probably either 8g or maybe 10g, depending on the CB needed.
    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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    DIY Member drizler's Avatar
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    Oh, I didn't even know they provided instructions with electric heater. That will do for me. If there's directions I can do about anything. I just get lost on those things that are left open to interpretation, local codes ect. Thanks for the advice.

  6. #6
    Plumber jimbo's Avatar
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    Most residential WH are 4500 watts, which on 240 is about 18,75 amps. 10 gauge will be required.
    Because of slower recovery on electrics, I would consider a 50 gallon.
    Forget the whirlpool. A 50 gallon tank, if you have it set hot, about 140, will give you 35 gallons of water at bathing temp. On a good day.

  7. #7
    DIY Member tk03's Avatar
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    I agree that a 50 gallon is definitely the size required but it will never heat your whirlpool tub. The tub may become unusable due to lack of recovery. A properly piped 30 gallon indirect water heater will recover way more than a fifty gallon electric.

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