Is it feasible to connect two hot water heaters to one fixture?

Discussion in 'Shower & bathtub Forum & Blog' started by jeff_bathroom, Mar 7, 2007.

  1. jeff_bathroom

    jeff_bathroom Member

    Messages:
    189
    Location:
    Florida
    Hi,
    I've torn everything out of my second bath and when
    I connect up the new tub, I'll be using hot water from a different
    water heater so that this bath doesn't share the same hw heater
    as the master bath.
    I wondered though if it is possible to connect both the original
    hot water line and the new one into a T, then into the tub hot water
    line? The idea of course being that there'd be almost twice the
    available hot water. Seems logical, but I guess I'm expecting a pro
    to tell me about some backpressure issues. What say ye?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,804
    Location:
    New England
    Possible, but maybe problematical. If the lines don't present similar resistance/restrictions, you might not get the benefit of the second source. There have been some recent discussions about running them in series vs parallel. You might want to search on that for some enlightenment!
  3. jeff_bathroom

    jeff_bathroom Member

    Messages:
    189
    Location:
    Florida
    Thanks Jim,
    I didn't know to search for "in series" or "in parallel", but after researching, I see lots of contraversy. Eeeegads, I'm not touching that one! One hot water heater it is. Although it would seem there should be some nifty little inline device that makes parallel heaters work without trashing them.
  4. leejosepho

    leejosepho DIY scratch-pad engineer

    Yes, somewhere there just has to be some kind of flow-control device (similar to a mixing valve) that will combine the two sources together in parallel, and likely with an adjustment for drawing more flow from one source than from the other, if desired.
  5. series for what you want

    hi jeff !!

    instead of plumbing them as separate systems, you can get the benefit of having more HW available in both baths and throughout the house, if you do a series installation. Series is a no-brainer. It is true that almost-simultaneous demand in both tubs might drain the last one of the series, which is the one likely to be set to the highest HW temperature. Not a big concern, imho.

    david
    Last edited: Mar 7, 2007
  6. jeff_bathroom

    jeff_bathroom Member

    Messages:
    189
    Location:
    Florida
    Sorry David,
    no in-series for me. Yours is one of the "pro" opinions of
    "in series" and there are plenty of folks who think in series is
    a bad idea along with those who think in parallel is bad or worse.
    Like Jim is agreeing above, there must be a pressure control device
    of some kind out there to run heaters properly in parallel. It either doesn't
    exist, doesn't work if it exists or we simply don't know about it.
    Anyway, in series seems to make more sense for new installations
    or cases when you're adding a second hot water heater rather
    than two that probably exist on opposite sides of the house like mine.
    Thanks for the opinion though; I'm always interested.
  7. Randyj

    Randyj Master Plumber

    Messages:
    1,047
    Location:
    Alabama
    I'm with David.... no way except in series... the second one holds the hot water and doesn't even have to come on to heat water until the first is depleted... you're getting twice the capacity and twice the capability without necessarily cranking up the second one. You have already begun recovery before the second one even begins to get cold.
  8. jeff

    thank you for telling me that the 2 HW heaters are 50 feet apart.

    There may be a few ways to get some connection that makes sense.

    Here is one idea: put a connector pipe -- and a valve -- between the new and the old HW heaters' output pipes, so that you can still have some flow to either tub when you need it. This is a manual override. You'd need a valve on each HW heater too. This is a parallel connection not series, and you control the flow by opening the valve when needed, instead of leaving it open all the time. Another advantage is that your house can operate on either tank whenever one of the two is out of operation.

    Another idea: this one needs a lot of valves. You connect to the input and outlets of one of the HW heaters, enough pipe and valves in an array so that you can have either parallel (as above) or series, depending on which valves you close.

    More ideas, that depend on existing "friction losses" (due to distances and elbows mostly) that will make more water go one way or another, if you connect the two. Depends on the layout in the rest of the house, and where your water enters your house.

    However, if you never run out of HW all this is unnecessary.

    david

    p.s. so far i haven't read anything against series connected HW heaters that i can recall that was serious.
  9. leejosepho

    leejosepho DIY scratch-pad engineer

    Prior to this thread, I had never heard of connecting two water heaters together ... and while I can see the balance problem in a parallel connection, I have also been pondering the effect of turbulence reducing the overall (combined) volume of hot water in a series connection. But, it just now strikes me that would probably not be an issue.
  10. jeff_bathroom

    jeff_bathroom Member

    Messages:
    189
    Location:
    Florida
    My workaround

    It's been awhile since I posted this.
    While plumbing my second bathroom, I realized that it's really just the showers that I wanted additional hot water for. So, I ended up installing two shower fixtures in the second bath...one connected to one hot water heater and the other connected to the second. Worked out just fine.
    Attached are some finished photos of the job. I really like having the two shower heads. My original plan was that it would be nice to have a second one in case I ran out of hot water on the first water heater. Turns out I just like to shower with both going. I don't shower at the same time as my wife so it's not an issue.

    Attached Files:

  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,251
    Location:
    Cave Creek, Arizona
    heaters

    It is a "no brainer" feed the second heater at the bathroom with the hot water from the first heater.
  12. jeff_bathroom

    jeff_bathroom Member

    Messages:
    189
    Location:
    Florida
    Well, I didn't mix them at the bathroom if that's what you're suggesting. The hot water feeds from each heater are still completely separate.
    I just ran the hot water from each heater to a separate fixture.
    And for me, it was a "brainer". :)
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,251
    Location:
    Cave Creek, Arizona
    heater

    I just ran the hot water from each heater to a separate fixture.

    More complicated and you did not really increase the amount of water available at any one fixture, which would have been the only reason to do it in the first place.
  14. jeff_bathroom

    jeff_bathroom Member

    Messages:
    189
    Location:
    Florida
    More complicated, yes; but not very complicated.
    The way I see it, the advantages are:
    * I get dual shower heads which is in the category of a "luxury shower" if I want one.
    * The original reason for doing this was so that I wouldn't run out of hot water. So, using the mixing method; if one water heater's hot water were used up or if the heater were broken, then it's going to mix its cold water with the other's hot water; defeating the original purpose.
    * I don't want to use hot water from the "secondary" hot water heater that supplies my wife's shower unless I want to. Using the mixing method, if we were to take showers at the same time; I would be using her hot water whether I wanted to or not. This scenario wouldn't happen very often unless we both take showers prior to going out to dinner or something. In that case, if I ate up her hot water, I'd be in deep doodoo.
    Guess the method depends on what you're trying to achieve.
    Thanks.
    -- Jeff
  15. alyka

    alyka New Member

    Messages:
    2
    i just read this thread and found some information that would help me in pimping my bathroom.... i will be installing a bathroom ceiling heater and im so excited about it.
  16. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,251
    Location:
    Cave Creek, Arizona
    heaters

    Your solution works if all you wanted to do was make sure either shower unit had a certain amount of hot water available. When its heater ran out of hot water, you will shower in cold water, but the other one will still have hot water. In a series installation, either shower would have TWICE the amount of hot water available, AND it would only create a problem for the second showerer if the first one were a glutton, in which case he deserves to get a cold shower the way you did do it. However, I might have connected BOTH of them to the hot water from the original heater.
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