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    New Construction Tankless Heating (12 Posts)

  • HomeBuyer HomeBuyer @ 7:04 PM
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    New Construction Tankless Heating


    I am in the process of buying a new construction property. Everything about the 1780 square foot townhome is great except I'm concerned about the Rinnai tankless heater being tasked with space heating plus domestic hot water.

    The space heating application is through one level of in-floor radiant heat and two levels of in-wall hydronic fan coils. It seems this application is becoming very common for new builds in the area.

    My question is if there is any way to mitigate the wear and tear on the unit. I am far from an expert in this area, but I believe this is installed as an open loop system (though perhaps indirect since I see a heat exchanger has also been placed on the wall?). For what it's worth, I'm also hopeful that the newly insulated home will retain heat fairly well.

    That said, can you ever add a wall mounted boiler (if space allows) to free up wear on the Rinnai? Or would it be more cost effective to ultimately plan to instal a combi unit in place of the Rinnai if / when it gives out past the 3 year warranty?

    Finally, are there any resources to understand what a combi system might cost as I factor that a potential future cost of the new home?

    Thank you!
  • Zman Zman @ 8:05 PM
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    Open vs Closed

    First let's figure out if it is open. There are health issues that go along with that one.
    Post some pictures
  • HomeBuyer HomeBuyer @ 9:00 PM
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    Thanks for the quick reply - much appreciated. Here are a few pictures of the set up.

    The picture with all four rows of the tubing was taken before the setup was fully complete, but the other two are final.

    You can't see a small heat exchanger that sits to the right of the Rinnai that seems to separate one pipe that runs to the rows of red tubes and one pipe that runs to the bottom row of blue tubes.

    Thanks again!
  • Zman Zman @ 10:49 PM
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    That is a closed system. That is good.
    You are correct that a water heater is not the same as a boiler. You have a budget system. Yes you could upgrade later with a combi boiler.
    I have never seen tubing that changes color from red to blue.It is best to not splice the tubing they obviously did.
     I am guessing it is potable water tubing with out an oxygen barrier. This is a problem if you have ferrous metal in the system. It is a sign of an inexperienced installer.
    Is the tubing in a slab?
  • Paul Pollets Paul Pollets @ 10:26 AM
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    At least the system has a FPHX for system separation. Unfortunately, non-barrier tubing was used on the radiant side. That means the FPHX will need to be used when appliance is replaced.
  • Rich Rich @ 10:37 AM
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    Potable Water Tubing

    If this heat exchanger and the circulator are not stainless steel you will have problems . Does this system have a pressure reducing valve and backflow preventer , I cannot identify that there is or is not one from the pictures , but I am damn near blind . O also don't see any air elimination which would certainly be a good thing due to the use of potable water tubing . This is possibly the first system I have ever seen where measures were taken (HX) to isolate open and closed portions from each other and then use tubing that allows air into the system   Carl and Paul , is that the PRV and BFP between the Expansion tank and HX ?
    You didn't get what you didn't pay for and it will never be what you thought it would
    This post was edited by an admin on November 17, 2013 10:40 AM.
  • Paul Pollets Paul Pollets @ 11:22 AM
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    Not enough detail to see all components. Don't see a 30# PRV on the system side of the FPHX. It seems to be piped for a manual fill.
  • HomeBuyer HomeBuyer @ 2:38 PM
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    Thanks for the thoughts - I appreciate the advice / questions as the final finishes are made to the property. I'll also try to take a more complete photo of the system.

    The pieces of information I do have is that individual tubes do not
    change color (though the photo may look like that since the tubes are
    close together). The bottom row is all blue (domestic water, perhaps?)
    and the upper rows are red.

    There is tubing in the slab for the
    ground floor radiant though I'm not sure what type since the home is
    nearly complete at this point and finished floor is in.

    Overall it sounds like my suspicion is correct and we should understand that this is not an ideal setup (though it at least seems some steps were taken to optimize the system). 

    It also sounds like the closed system is the best method for this application - though I believe this means the Rinnai warranty is not valid. Should I expect a few years out of this system followed by a combi install? I don't think I'll have success asking the builder for a new heating unit altogether, though perhaps I can push to ensure we have items such as the stainless steel components, pressure reducing valve and backflow preventer.
  • Rich Rich @ 2:57 PM
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    The installer

    seems to have set up the system using red for supply (hot) and blue for return (cool) . This can only be done by joinng lengths of red and blue tubing therefore creating a buried joint or possibly joint not buried but in either case a potential leak path that was otherwise not necessary . The upper and lower rows are both space heating .    The mixing valve directly below the heater is your hot main and the pipe coming into that valve from the right is cold potable water .
    You didn't get what you didn't pay for and it will never be what you thought it would
  • Gordy Gordy @ 3:39 PM
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    blue tubing manifold

    is the return for the supplies of the radiant loops.

    Deduction from what can be seen is 7 radiant supply loops off of the 3 manifolds, and 7 returns on one manifold. if this is true then the tubing changes color somewhere with a splice.
  • Rich Rich @ 3:52 PM
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    notice that this system piping configuration has changed in the pic w/o controls to the pic with controls ? The top 2 loops supply in the first pic is fed directly through the run of a tee and the latter pic has a 90* feeding that supply .
    You didn't get what you didn't pay for and it will never be what you thought it would
  • Gordy Gordy @ 5:37 PM
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    Yes Rich

    I noticed that.
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