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Thread: Hot Water heater sizing question

  1. #1
    DIY Member ron in sc's Avatar
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    Question Hot Water heater sizing question

    I need to install water heater for detached garage, it will have to be electric.

    How big a tank to I need? It will need to supply hot water to following:
    -front loader washing machine, used only to wash items used in connection with use of garage
    -sink
    -shower; which will be used infrequently
    -outside spigot; also used infrequently

  2. #2
    Plumber jimbo's Avatar
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    A 30 gallon would be fine for the WM and shower, although a 40 doesn't cost much more.

    A hose bibb will suck an 80 gallon dry in about 4 minutes!

  3. #3
    DIY Member ron in sc's Avatar
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    A hose bibb will suck an 80 gallon dry in about 4 minutes!
    I do have a spigot next to it that is regular water, if I do use the hot water to wash really dirty stuff like boat it sounds like I should make a connnection between the two so I can mix the hot water with the cold.

    Also what do you think about those hot water heaters that have can be set for a few different modes. One of the house hot water heaters has that it's a Whirlpool and has this thing on top that say energy smart. Are they just a gimmick? Maybe one of those would be good in the garage too.

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    DIY Member Squ1rrel's Avatar
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    Those energy smart panels are supposed to track usage and only keep water hot during the times you most use it...not sure how well it would work if you use different amounts at changing times. Plus it's a Whirlpool..with all the problems with their gas WH's, I'd be leery of their electrics too.

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    In the Trades Bob NH's Avatar
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    Quote Originally Posted by ron in sc View Post
    One of the house hot water heaters has that it's a Whirlpool and has this thing on top that say energy smart. Are they just a gimmick? Maybe one of those would be good in the garage too.
    "Energy smart" on an electric water heater is a gimmick. They have such good insulation, and such poor recovery rate, that controlling the heating on a 24 hour cycle would be a hopeless exercise.

    The only "energy smart" that would mean anything would be if you were getting a special rate from the power company for off-peak power. If that is the case there should be a power company clock system that would allow them to shut off the lower element during peak (high rate) times.

  6. #6

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    50 gallon may be as cheap or very nearly the same price as a smaller heater. Paying more for efficiency is a very good idea - better insulation saves money. Paying for silly electronic gadgets and hype is not a good idea. (Not yet, anyway. Maybe someday they'll actually implement such things effectively.)

  7. #7
    DIY Member ron in sc's Avatar
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    A 30 gallon would be fine for the WM and shower, although a 40 doesn't cost much more.
    Is it cheaper as far as electricity goes to use a smaller tank, since it should take less electricity to keep less water hot?

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    Not necessarily. The exterior surface area difference between different size water heaters isn't quite linear, so a bigger WH has less exterior surface area to radiate out heat from than a smaller one. The quantity and quality of insulation makes a big difference. WIth an electric WH, you have nearly 100% efficiency in heating, but your standby loss is determined by the quality of the insulation and the area that acts like a radiator.
    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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    I'd go with the 50 gallon, you must have a nice setup, and or income to have a detatched garage with a washer and dryer just for the garage. but hey more power to you.

  10. #10
    Master Plumber master plumber mark's Avatar
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    Talking get the 50 and install a breaker switch.

    Get the 50 gallon and put the blanket on it...

    Stay AWAY from that Energy smart heater...,,
    it is a piece of junk and will eventually give you troubles
    http://www.weilhammerplumbing.com/galleryi/

    Get a GE from HD


    Now if you really want to save energy in the garage,

    install a breaker or a breaker junction box with a lever
    right next to the water heater....
    and just turn the water heater on only when you need to
    on the weekends or an hour before the action begins....
    instead of heating the water 24 hours a day.....

    it will literally heat up in about a half hour ..
    .

  11. #11
    Master Plumber Redwood's Avatar
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    Quote Originally Posted by master plumber mark View Post
    Now if you really want to save energy in the garage,
    install a breaker or a breaker junction box with a lever right next to the water heater....
    just turn the water heater on only when you need to
    on the weekends or an hour before the action begins....
    instead of heating the water 24 hours a day.....
    it will literally heat up in about a half hour ..
    Sounds like the perfect environment for legionella!
    The water should be in the prime growth zone for about all week!


    On a lighter note I would suggest this sillcock for hot/cold water mixing. Just using a wye hose cold be a cross connection that among other things could crack a toilet. http://www.moen.com/products/HC400508


  12. #12
    Master Plumber master plumber mark's Avatar
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    Talking you think it would ???

    I never considered some funkey bacteria
    growing in the tank......even on city water

    I suppose that is a possibility, however so slight...

  13. #13
    Master Plumber Redwood's Avatar
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    I do not advocate turning off the heat on a water heater. This will increase the danger if Legionaires desease.

    The biggest single threat from tepid water is probably legionella.

    70 to 80 C (158 to 176 F) - Disinfection range
    At 66 C (151 F) - Legionellae die within 2 minutes
    At 60 C (140 F) - Legionellae die within 32 minutes
    At 55 C (131 F) - Legionellae die within 5 to 6 hours
    50 to 55 C (122 to 131 F) - They can survive but do not multiply
    20 to 50 C (68 to 122 F)- Legionellae growth range
    35 to 46 C (95 to 115 F) - Ideal growth range
    Below 20 C (68 F) - Legionellae can survive but are dormant

    http://en.wikipedia.org/wiki/Legionella

    Many of the states and at least some of Canada are now requiring water heaters set at 140 Degrees F and a tempering valve on the outlet to lower the water temp to 120 Degrees F. I would expect that this will be a code requirement everywhere before long.

    Have a look see at this link... http://www.cashacme.com/legionella_main.php

    Last edited by Terry; 01-28-2011 at 05:00 PM.

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