How to change water heaters from parallel to series?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by AllanChang, Jun 29, 2020.

  1. AllanChang

    AllanChang New Member

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  2. AllanChang

    AllanChang New Member

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    I shuted off either of the cold water inlet valve, there was no hot water output any more. I thought if I turn off the gas/cold water inlet of left tank, it will be in series model, but it did not work. We only have 3 persons in the house, so really do not need these two 90 gallons heaters to work at the same time.
     
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  4. hj

    hj Moderator & Master Plumber Staff Member

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    They are already in "series" so you CANNOT shut just one off, and they look like 50 gallon heaters, escecially since they have never made 90 gallon ones. If you only need one heater turn off the gas control on the right hand one and leave everything else as it is.
     
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  5. Sylvan

    Sylvan Still learning

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  6. AllanChang

    AllanChang New Member

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    @hj, thank for your reply. I will try to shut off gas on the right one. Given the hot water outlet is on right tank, suspect the water will not be hot as before?
     
  7. Reach4

    Reach4 Well-Known Member

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    Those would be some unusual water heaters in that case. When you face the label and the gas valve, hot is on your left in all of the WHs I have seen.

    Check it. Maybe your WHs have been piped in backwards.
     
    Last edited: Jun 30, 2020
  8. fitter30

    fitter30 Active Member

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    Heaters piped in series the first tank will fail first because any mineral built up gets deposited there. When changing the system to parallel the return pump should be piped into the left heater also.
     
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  9. Sylvan

    Sylvan Still learning

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    Equipment being equal, two or more heaters connected in parallel will deliver more hot water than the same heaters connected in series. In a parallel configuration, the hot water demand is taken equally from each unit. ... Each heater will then perform the same amount of work to heat the cold water.
     
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  10. AllanChang

    AllanChang New Member

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    it's weird setup, I am still confused if this is series or parallel, as the cold water goes into both tanks, but hot water only out on right tank. I will not turn off gas on right tank because the water will be cold when going out. now I've changed the temperature setting on left tank to low, and right tank to hot, any problem for this?
     
  11. Reach4

    Reach4 Well-Known Member

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    I see that extra connection to the drain port on the right-side tank. That is probably a hot water recirculation line.

    You don't buy that the cold input for a WH should be on the top right?
     
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  12. AllanChang

    AllanChang New Member

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    on the top of both tanks are the cold water inlet, there is only one port of hot water outlet, i.e. on the drain port of right tank
     
  13. Reach4

    Reach4 Well-Known Member

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    There are two water pipes atop each WH. What should be the hot out of the right tank is feeding the cold input of the left tank via that copper pipe.

    It may be that whoever hooked up these tanks piped them backwards.

    It looks like the hot water recirculation can be stopped (or tuned) with those two black-handled valves. You should unplug the recirculation pump if you want to close those valves during your investigation.
     
    Last edited: Jun 30, 2020
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  14. AllanChang

    AllanChang New Member

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    Thanks for looking at it. I will do more investigation.
     
  15. Helper Dave

    Helper Dave New Member

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    Run some hot water in the house, and touch the left pipe on the left heater. It will be hot, since that's where the hot water comes out.

    The pipe going into the drain on the right heater may also be hot, but it is a recirculation line, which pumps cooling water from your hot water lines back into the water heater at the bottom of the tank so it can be reheated (Hot water rises. Cold water is delivered to the bottom of the tank.). The recirculation pump is that thing on the pipe to the left of that wall outlet.

    Turning the gas off on the right heater will just turn it into an expensively plumbed storage tank, while the left tank will do all the heating.

    Leaving two tanks would make for an inefficient system, especially with that recirc line. I would recommend having a plumber come in, and disconnect the left tank, and repipe for a single tank.
     
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  16. AllanChang

    AllanChang New Member

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    thank you so much Dave! I think I understand how it works now after your explanation:). yes you are right the pipe on the top of left tank is the hot water output, and the pipe on the drian port of right tank is for recirc.
     
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