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Thread: Multiple water heaters needed

  1. #1
    DIY Junior Member Habitat.pat's Avatar
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    Default Multiple water heaters needed

    I have a house with 2 jetted tubs and 2 separate showers, plus another tub. One of the jetted tubs is enough to come close to draining the 50 gallon water heater that is currently installed. I can't fit a larger water heater up the pull-down stairs into the attic, so I was thinking of replacing the current water heater (old) with 2 new 50 gallon heaters.

    There is a 1" gas supply line into the area, so that shouldn't be a problem.

    My question is how to interconnect the two water heaters to get the best use out of them.

    I could connect the output of the first heater to the input of the second heater and set the 2nd heater's temperature a bit lower than that of the first one. That way when the first heater starts to run low on hot water the second one would turn to add some heat. The problem as I see it with this setup is that the first heater would get much more use than the second one.

    I could parallel the two water heaters, but getting the temperatures set the same would be quite a trick.

    Instead of adding a second water heater I could add a storage tank with heat siphoning to circulate water from the tank back to the water heater to keep it hot, but it seems that a tank would probably cost more than a second water heater.

    I can't split the hot water pipes to put part of the system onto each heater, the tees are all in the walls or finished floor.

    Any ideas?

    thanks,
    Pat

  2. #2
    In the Trades Bob NH's Avatar
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    Setting the temperatures would probably be easier than balancing the flows if they are connected in parallel.

    The first heater (the one with the cold water feed) is almost always going to get the most work because it will immediately try to heat the water. The second heater will maintain its temperature and will raise the water temperature when the high demand exceeds the capacity of the first heater.

    The two heaters will have double the recovery rate when you have high demand. That is the advantage of having two heaters versus one heater and a storage tank. If you just want a storage tank you could use an electric heater set at a temperature a little lower than the first stage gas heater. I think you will get less heat loss from an electric heater, but you will lose the advantage of the higher recovery rate and lower energy cost of the gas heater.

    If you are going to have the capacity you are buying with the second heater, you will want them both at the operating temperature that you need to supply your demand.

  3. #3
    Plumber jimbo's Avatar
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    I would have a contractor look at the structure before putting ANOTHER 550 pounds of weight on the ceiling joists.

  4. #4
    DIY Junior Member Habitat.pat's Avatar
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    Quote Originally Posted by jimbo
    I would have a contractor look at the structure before putting ANOTHER 550 pounds of weight on the ceiling joists.
    This is not a problem, the water heater(s) sit directly over the junction of two interior walls.

    Besides, I've done home building for close to 20 years and can make that call myself. Thanks for the concern though.

    Peace,
    Pat

  5. #5

    Default

    I am kind of new around here but how about a tankless heater?

  6. #6
    Master Plumber master plumber mark's Avatar
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    Talking two heaters

    dont fool with the tankless, they dont have the
    volume controll for high demand situations


    jsut do what you are doing and you will be ok..
    2 50 gallon heaters in series will
    work pretty well.

    take the water into the first tank then
    feed the second from the first then feed the house
    from the second....


    set the first tank on med.. to pre heat the water
    set the second one on hot...

    that is a lot of how water.... be sure to add
    a thermal expansion tank somewhere and
    be sure to take the t+p pipes to a drain if
    one is available...


    your only issue might be a large enough flu pipe

  7. #7
    Moderator & Master Plumber hj's Avatar
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    Default hot water

    Two 50 gallon water heaters in series with both set at the same temperature will give you what you want. You only heat the water you use, except for the tank's heat loss which will be about the same regardless of the temperature, so you do not get any benefit, and will in fact lose some benefits by having different temperature settings. The first water heater will fail more frequently, but no sooner than if it were the only one.

  8. #8
    DIY Junior Member Habitat.pat's Avatar
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    Quote Originally Posted by hj
    Two 50 gallon water heaters in series with both set at the same temperature will give you what you want. You only heat the water you use, except for the tank's heat loss which will be about the same regardless of the temperature, so you do not get any benefit, and will in fact lose some benefits by having different temperature settings. The first water heater will fail more frequently, but no sooner than if it were the only one.
    Thanks for the information.

    Would there be any bebefit to interconnecting the heaters at the drains to allow for water flow between the tnks via thermal pumping?

  9. #9
    DIY Junior Member Habitat.pat's Avatar
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    Quote Originally Posted by master plumber mark

    <snip>

    your only issue might be a large enough flu pipe
    I'm not sure we are allowed to combine flues here, I'll check with the inspectors. It would probably be easier to just run the new flue through the roof, it's only 5' above the heaters.

    T/P lines will be run out individually, but I plan on connecting the water heater pans to the existing 3/4" drain line.

  10. #10
    In the Trades Bob NH's Avatar
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    "Would there be any bebefit to interconnecting the heaters at the drains to allow for water flow between the tnks via thermal pumping?"

    That would be a bypass from the inlet of one to the inlet of the other. I don't think you would get much thermal pumping, and it would be uncontrolled. I like to connect things so I know where the flow is going.

  11. #11
    General Contractor Carpenter toolaholic's Avatar
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    Default my 2 cents

    ceiling storage is good for xmass decoration storage

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