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Thread: Winter - Summer Hook Up

  1. #1

    Default Winter - Summer Hook Up

    This post relates to boiler, tankless heaters and hot water heaters, and my main question is whether what I want to do is allowed so I posted it in the plumbing forum - I hope that's right.

    I have a steam boiler with a hot water coil, a gas h/w heater and a tankless water heater. I want to set them up so that I use the tankless in the summer and the boiler coil/gas hot water heater in the winter.

    The gas hot water heater will be piped so that the cold supply goes into the boiler coil. The boiler coil out will go to a mixing valve, then to the cold inlet of the gas hot water heater.

    Is this legal? I'm wondering if it is because the boiler coil and gas hot water heater loop will be stagnant in the summer. It shouldn't be a problem as long as they are drained each summer (and the tankless in the winter) but I'm not sure this set up is permitted by code.


  2. #2


    Your going to have to hire a LICENSED plumber for this task, This is not a "DIY" kinda thing

    But in would depend on local code and the plumbers out there.

    Like, I said, Call a plumber and see what they tell you, They will actually be there to see whats / what....anyhow.

    You Should Assume Everything I say Is A Complete Lie - Thank You ~

  3. #3


    plumbinkskool I appreciate your taking the time to answer but that wasn't the question.

    I realize this is my first post here so you guys have no idea if I know what I'm doing, but let me assure you it isn't a matter of skills, etc. I'm not your average DIY'er - I've built two kitchen additions (everything except the foundation) on two different homes, remodelled several bath rooms, a basement, etc.

    I just want to know if my plan is a legal one before I go to talk to the city inspector because I don't like to show up to a meeting without knowing what I'm talking about.

    Thanks again.

    ps - I'm not asking about the boiler coil/gas hot water heater combo - that's already installed and passed inspection when I hooked up the boiler. What I want to do now is add the "summer loop" of the system - the tankless water heater.
    Last edited by jwilson; 05-11-2009 at 07:13 PM. Reason: Added the ps

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    I think I'd put a T on the inlet to the WH and run the outlet of the coil in the boiler to both the WH and the Tankless. Put a shutoff on each inlet and outlet and rejoin them on their outputs.

    If you drained the WH, the rest would be getting refreshed. Won't hurt the boiler coil to be used even if the boiler isn't on. If you needed more hot water, you could try running both the WH and the tankless. Not sure how well that would work with the differences in relative flow since most tankless systems have more internal restrictions.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default heaters

    Just do it. Use a three way valve in the feed to the heaters to switch the flows and you will not have to worry about whether you turned the right valves.

  6. #6


    Thanks for those replies guys.

    jadnashua not sure if it's ok to put have that hot an input on the tankless, I think's it's minimum BTU input might overheat the water. I'll have to check the manual.
    They won't be near each other though because the two are on opposite sides of the house - which is also one of the reasons I'm putting in the tankless; the chimney (boiler and gas hot water heater)is on the west wall and ALL water fixtures are on the east wall, which is where I located the Rinnai.

    I like HJ's suggestion best - "just do it".

  7. #7
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default heater

    I assume you would turn off the gas to the tankless so it would just be a pass through, although if it had a flow restrictor to limit the velocity then it could compromise the flow at the faucets.

  8. #8


    The tankless gas is a 3/4" branch off of a 1" header. And would simply be shut off.

    The tankless water heater is also a branch so that when it's off the cold water would bypass it and go to the boiler/ hot water heater. Thus flow to hot fixtures would actually reverse in the same pipes. Attached is a sketch of the system.
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