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Thread: Water heaters piped in parallel

  1. #1
    DIY Junior Member greekguy7's Avatar
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    Default Water heaters piped in parallel

    I have 2 50gallon hot water heaters piped in parallel for a 6unit apartment building. A few days before Christmas I replaced one of them because it was leaking, but not the other. (mistake number 1). The new hot water heater is now several inches higher than the older one.

    Doing some "pipe-grabbing" while a hot faucet is on, it looks like the new one is being used a little more than the old one although both are running. I tried closing the ball valve on the output of the new one just a little to create some restriction so I can balance the two water heaters out. Any drawbacks to this??

    I do plan on replacing the older one as soon as I get a chance.

  2. #2
    Master Plumber master plumber mark's Avatar
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    Talking do it in series

    you would be best to just change itto series and

    forget about it......

    series works best in about every situation...

    you absolutley KNOW that it will give you 100 gallons of
    water no matter which heater begins to clog up first....

  3. #3
    Plumber/Gasfitter dubldare's Avatar
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    --Customers of plumbers: Never be afraid to ask for proof of licensure of the plumber servicing your equipment. A licensed plumber will be proud to show you his personal license.--

  4. #4
    Master Plumber,Mech Contractor aphco's Avatar
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    Cool Check it out!

    Just found this forum and just joined.

    Greek Guy7, do some research before you replace your heater. Every heater manufacturer that I know of advises that the best set-up is a parallel installation.

    We have always installed heaters in parallel and have never had a problem. We have also changed installs from series TO parallel and it always cures the problems. Also when installing more than 2 heaters they are done in parrallel.

    Series is not as efficient and does not allow shutting off one heater at a time if there is an outage or a leaker. With series you might as well have only one heater because when one goes out they both have to be shut down.

    The important thing is to remember to balance the piping so that the resistance is the same for each heater and the draw is equalized.
    Last edited by aphco; 02-21-2007 at 06:01 PM.

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    Master Plumber master plumber mark's Avatar
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    Talking series simply works best

    this last guy stated at the end of his post....

    The important thing is to remember to balance the piping so that the resistance is the same for each heater and the draw is equalized.[/quote]

    gee...is that all I got to do??


    The problem is over time the heaters start to corrode
    at the inlets and clog up through the dialectric unions..........
    and you get more draw from one than the other...

    if your parrell piping is of just a half an inch off from perfect,
    you will get more draw from one over the other....


    then when one water heater goes out....you MUST replace it with
    the EXACT same heater 10 years from now or your draw
    will not be exactly the same between them....


    like the problem this fellow faces right now....

    he just cant replace a heater plumbed in parrell..with just any
    heater off t he street...and expect it draw
    right......

    been there ...done that ....and got the tee shirt too.....

  6. #6
    DIY Member jluksic's Avatar
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    In support of Series...

    Dubldare's pdf link implies that both parallel water heaters are set to equal temperatures - which causes the first WH to wear faster. I think most WHs in Series are configured to step the temperature, the first raising the temp to ~75F and the second to final temp ~ 140F.

  7. #7
    Master Plumber,Mech Contractor aphco's Avatar
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    Quote Originally Posted by jluksic
    In support of Series...

    I think most WHs in Series are configured to step the temperature, the first raising the temp to ~75F and the second to final temp ~ 140F.
    1) I'm new to this forum, but not to plumbing and I hate to disagree, but,I suggest that you check the water heater manufacturers' websites and see if any advise the use of a series installation. If so please post a link.

    2) Setting a water heater to only 75 degrees ( if the thermostat will even go that low) will set up a heck of a condensation problem and rot out a heater way before its time.

    3) It is not an exact science, but you can match the piping lengths on the original install and in the future use a water heater that comes as close as possible to the old heater.

    4) Especially in multi-family dwellings the parallel installation gives you the ability to have one heater out of service and still use the other until the bad one is replaced. Try that with a series install.

    5)If dielectric unions are plugging up, don't use them. Use a brass union and a brass nipple to keep the water way clear. Even though dielectric unions are approved they cause more trouble than they prevent.

    6)Explain to me how you successfully hook up 3 water heaters in series and provide fpr individual shut offs. Easy to do in parallel.
    Last edited by aphco; 02-22-2007 at 05:14 PM.

  8. #8
    In the Trades kordts's Avatar
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    Default

    I can explain how I pipe in series and can shut down one of the heaters. You pipe a bypass with 5 valves and you're good to go.

  9. #9
    Master Plumber master plumber mark's Avatar
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    Talking by-passing on series

    like the Mr Kords fellow said,,,

    its just a matter of simply putting a by-pass across
    the top of each water heater each water heater
    will ball valves.... just like a water conditioner.....

    on two heaters you would need 6 ball valves...

    3 for each heater......one horizontal across and two verticle in and out

    and maybe an extra one
    before it comes to the heaters if you wish....

    nothing has to be "exactly the same in length"

    you CAN replace one heater years later with any brand you want
    and you dont have to worry about draw.......

    so what makes this----- brain surgery????


    as far as setting the temps, I think the first heater
    should be set about 110 and the second one to be
    set at 125+

    ans you will have a continous feed of 100 gallons

    you really cant go wrong..
    Last edited by master plumber mark; 02-23-2007 at 04:29 AM.

  10. #10
    DIY Junior Member mike08201's Avatar
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    Quote Originally Posted by master plumber mark
    you would be best to just change itto series and

    forget about it......

    series works best in about every situation...

    you absolutley KNOW that it will give you 100 gallons of
    water no matter which heater begins to clog up first....

    In total agreement on that! I'm just a rookie but I can speak from first hand knowledge on this issue.
    When I had my old oil fired boiler it had the coil for hot water, never quite did the trick to my satisfaction. So I bought an electric 40 gallon and had the boiler feed it with pre-heated water and the electric took it the rest of the way. (In series)
    I NEVER ran out of hot water, it was great. Then we coverted to gas and i lost my hook up <sigh>
    I miss the old days LOL

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