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Thread: Any experiences with the Bosch AE 125 (Electric) Tankless?

  1. #16
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by STyler View Post
    However, I can't find a way to get the volume of hot water I need to wash my horses without draining the tank.
    A 2 GPM shower = 16# of water per minute
    Raised 50F would take 800 BTU/min = 48,000 BTU/hr = 14 kw. Most water heaters use 9 kw.

    You'd need 60 A @ 240v and this would leave the water temp in the tank the same as it was before the shower, so this is a max and it's what a tankless would draw, if I haven't made any arithmetic mistakes.

    How many gallons of how hot water do you need?

    What is the lowest incoming water temp?
    Last edited by Thatguy; 10-23-2009 at 05:14 PM.

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    Master Plumber master plumber mark's Avatar
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    Talking sorry about the bind in your shorts

    hooking two elements up to run together will require
    much more power than 220... you are getting into a commercial application type water heater...

    you cant do that without blowing the breaker, heating up the wire ect.... it wont pull enough to heat up 2 4500 watt elements ......

    ...

    if you already have a 50, go out and buy an 80, and hook them up in series...

    you will have to run another 220 line , and you
    can also just turn them off when not in use .

  3. #18
    Plumbing Designer FloridaOrange's Avatar
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    Electric tankless takes a huge amount of power if you want a good amount of flow. I prefer tank type with electric.

    Since this sounds like a remote situation, have you considered a gas tankless? You could run it off of a decently sized LP tank.
    Matt
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    Quote Originally Posted by Thatguy View Post
    A 2 GPM shower = 16# of water per minute
    Raised 50F would take 800 BTU/min = 48,000 BTU/hr = 14 kw. Most water heaters use 9 kw.

    You'd need 60 A @ 240v and this would leave the water temp in the tank the same as it was before the shower, so this is a max and it's what a tankless would draw, if I haven't made any arithmetic mistakes.

    How many gallons of how hot water do you need?

    What is the lowest incoming water temp?
    Not sure how many gallons - but it'll be far in excess of 2 GPM. I'll have a non-restricted 3/4" supply of hot and cold to the mixing valve and a virtually unrestricted sprayer. It takes about an hour per horse, and while the usage is pretty heavy, it isn't constant.

    Power isn't an issue - I have plenty available.
    Last edited by STyler; 10-23-2009 at 05:52 PM.

  5. #20
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    Quote Originally Posted by STyler View Post
    Not sure how many gallons - but it'll be far in excess of 2 GPM. I'll have a non-restricted 3/4" supply of hot and cold to the mixing valve and a virtually unrestricted sprayer. It takes about an hour per horse, and while the usage is pretty heavy, it isn't constant.

    Power isn't an issue - I have plenty available.
    First cut: 80 gals @ 160 F combined with 80 gals @ 50 F gives you 160 gals @ 105 F.
    How cold can the shower be?
    Will 160 gals wash one horse?
    Once the BTU/hr output is established there are many ways to supply this many BTUs input over hours or days preceding the shower. The heat can be stored in water or iron or whatever. You probably want to stay under 160 F for water but with iron you can pretty well heat it as hot as you need.
    Last edited by Thatguy; 10-23-2009 at 07:51 PM.

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    Quote Originally Posted by Thatguy View Post
    First cut: 80 gals @ 160 F combined with 80 gals @ 50 F gives you 160 gals @ 105 F.
    How cold can the shower be?
    Will 160 gals wash one horse?
    Wish I knew. I'm just planning on providing overkill so I don't have to worry about it. I'd guess wash temp would be closer to 95-100 F.
    Last edited by STyler; 10-24-2009 at 04:46 AM.

  7. #22
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    Quote Originally Posted by STyler View Post
    Wish I knew. I'm just planning on providing overkill so I don't have to worry about it. I'd guess wash temp would be closer to 95-100 F.
    OK, so 5 GPM with half the water supplied by a heater set at 160 F would give you a ~30 minute shower.
    Two 80 gal tanks would give you one hour.

    Or, if you can get heater elements that put ~35 kw into your 80 gal tank you have in effect made yourself a 5 GPM 100 F "tankless" heater.
    The problem now is to find a 35 kw, 146 A, 1.6 ohm heating element that is mechanically compatible with your existing heater. You probably won't find one; it would get so hot the water would boil locally and impede heat xfer.

    Another way, using any 300 gal. tank holding 2500# of water.
    It takes 1.3 therms, 37 kwh, to heat this 300 gal by 50 F.
    At 4500w from your regular WH it takes 8 hrs @ 0.6 GPM to fill the tank with hot enough water.

    To avoid math errors and do tradeoffs put this on a spreadsheet.
    Last edited by Thatguy; 10-24-2009 at 09:38 AM.

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    Is having the water heater wired for simultaneous operation an option to reduce recovery time?

    Side note: Why do the WH mfg'ers show the annual operating costs of 40, 50, 65 and 80 gallon units all roughly the same (just a few dollars difference)?

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    Quote Originally Posted by STyler View Post
    Is having the water heater wired for simultaneous operation an option to reduce recovery time?
    Twice the input power = half the recovery time.

    Side note: Why do the WH mfg'ers show the annual operating costs of 40, 50, 65 and 80 gallon units all roughly the same (just a few dollars difference)?
    Two of us use 35 therms/month to heat the water. The WH gallon size may not correlate that well to family size. Normal use is 70 gal/person/day of water. Maybe half of that is hot water.
    I guess there could be some Economy of Scale with larger heaters.

    Or, they're just lying.

  10. #25
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    Quote Originally Posted by STyler View Post
    Side note: Why do the WH mfg'ers show the annual operating costs of 40, 50, 65 and 80 gallon units all roughly the same (just a few dollars difference)?
    Typically residential units, regardless of tank size, use (2) 4.5KW elements.
    Matt
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  11. #26
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    Quote Originally Posted by Thatguy View Post
    Two of us use 35 therms/month to heat the water. The WH gallon size may not correlate that well to family size. Normal use is 70 gal/person/day of water. Maybe half of that is hot water.
    I guess there could be some Economy of Scale with larger heaters.

    Or, they're just lying.
    Thanks for the help.

    Going to try and make a tank work. Then just wait and see if I need to add to the system.

  12. #27
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by STyler View Post
    Side note: Why do the WH mfg'ers show the annual operating costs of 40, 50, 65 and 80 gallon units all roughly the same (just a few dollars difference)?
    Because the Energy Guides are written for an average U.S. home's estimated hot water use, regardless of water heater size. (I think 2.6 residents is one of the assumptions.) Actual use will vary widely by region because of annual average incoming water temperature, not to mention individual habits, etc. With a family of four in a midwestern climate I use only about 60% of the Energy Guide total and a quarter of that is standby losses.

  13. #28
    Forum Admin, Expert Plumber Terry's Avatar
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    One of my customers uses an Electric Tankless for washing wine barrels.

    Like you, he needs an endless supply of heated water.
    Once the job starts, he's washing until every last barrel is clean.
    He has a winery, and I've seen how many barrels he has to clean.
    The other wineries in Woodinville use tankless too.
    If you use electric, the electrician brings in the proper breakers and wire for it.
    They use much more power then a two element tank heater.
    A two element tank heater only heats with one element at a time.
    So unless you have plenty of stored heated water beforehand, you will run out.
    Or you can also use gas.

    I specifically added a 200 amp service instead of 100 amp because of the requirements of this model.
    Last edited by Terry; 10-30-2009 at 10:51 AM.

  14. #29
    In the trades Dana's Avatar
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    Quote Originally Posted by Terry View Post
    One of my customers uses an Electric Tankless for washing wine barrels.

    Like you, he needs an endless supply of heated water.
    Once the job starts, he's washing until every last barrel is clean.
    He has a winery, and I've seen how many barrels he has to clean.

    The other wineries in Woodinville use tankless too.
    If you use electric, the electrician brings in the proper breakers and wire for it.
    They use much more power then a two element tank heater.
    A two element tank heater only heats with one element at a time.
    So unless you have plenty of stored heated water beforehand, you will run out.
    Or you can also use gas.
    As an aside, high volume continuous flow washing apps like this are where drainwater heat recovery systems can often pay big dividends, boosting the apparent-power of the HW heaters by 6-10kw while cutting the power use in half. (Probably easier to consider retrofitting into a winery than in a stable though, eh? ;-) )

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    It's very difficult to get water usage requirements from my daughter, but after grilling her, it appears that the usage during that 1 hour per horse wash cycle is not as constant as I initially thought.

    Since I have a near-future need for a 50 gallon tank heater, I think I'm going to try that unit in the barn and wire it for simultaneous element operation and see if that is a workable (and much cheaper) option for the barn. If it can meet the demand, I'll leave it in, if not, I'll switch over to tankless and use the 50 gallon unit in another application.

    Currently looking at the Rheem Model# 83MXR52-2 (if I can find a supplier or Home Depot sells a GE equivalent). Anybody know of any issues with this model in simultaneous operation?

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