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Gas Instantaneous Water heater and Radiant floor?...BP

Client is thinking of replacing an electric water heater used to supply heat to a small 1950s slab radiant floor (rest of house is scorched air) with a direct gas fired instantaneous unit. Wondering how well this works, what to look out for, and recommendations? Thanks all for all you do!


Boilerpro

Comments

  • Dana
    Dana Member Posts: 126


    I think you'll have temperature control problems. The instantaneous gas sytems fire by way of a flow valve and modulating gas valve. I'm not sure you could get enough flow through the unit with a circulator to even fire it. And if it fires it would probably hit temperature pretty fast and shut down. Maybe with a storage/buffer tank you could do it.
  • Bill Riordan_3
    Bill Riordan_3 Member Posts: 31
    Flow

    I agree, I've seen many installs where correctly sized circulator on the radaint loop produces G.P.M. too low to ignite burners. Trying to raise G.P.M. will cause radaint loop to perform poorly. Just my thoughts.

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  • Boilerpro_2
    Boilerpro_2 Member Posts: 89
    Those were my concerns too

    Sounds like a small gas fired tank may be the way to go. Anything out there like the combicore, without some of the reliability problems I've heard about?

    Boilerpro
  • Michael B
    Michael B Member Posts: 179
    I just

    saw something come over my desk from Triangle-tube. Let me see if I can find something on the web...

    Michael Bleier
    Able Distributors
    www.abledistributors.com
    "The Supplier Who Works With You"
  • Michael B
    Michael B Member Posts: 179
    here is the

    link to Triange tube combi units

    http://www.triangletube.com/redirect/frdirwaterheater.htm

    good luck,

    Michael Bleier
    Able Distributors
  • Boilerpro_2
    Boilerpro_2 Member Posts: 89
    Thanks, I'll have a look. NM

  • Josh M.
    Josh M. Member Posts: 359
    Hold up

    I have used a Rinai instant hot with a modulating gas valve in small applications before. The problem is you can only go up to something like 7-8 GPM. The unit only needs about .5gpm to fire. If you need to increase the GPM through your radiant zone obviously you can do that on your secondary loop. I have found these units to be actually a much needed product for condos and cabins. It is great because it modulates between 19-180 btuh/hr giving it about 87 percent efficiency.
  • hot_rod
    hot_rod Member Posts: 22,771
    I've heard 6 gpm

    max on the Rinnai, with the highest head pump money can buy :)

    Also there was an issue with the burner modulating back when it started seeing warm return temperatures. The dealer here said a special "radiant application" board was in the works to correct this. Maybe it is available now.

    It's the pressure drop through the HX that limits most instantanous/ radiant. Also the code approvals in some areas.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream


  • > I think you'll have temperature control problems.

    > The instantaneous gas sytems fire by way of a

    > flow valve and modulating gas valve. I'm not sure

    > you could get enough flow through the unit with a

    > circulator to even fire it. And if it fires it

    > would probably hit temperature pretty fast and

    > shut down. Maybe with a storage/buffer tank you

    > could do it.



    Definitely either buffer tank or make sure you get a unit specifically made for radiant. Using a lot of instantaneous water heaters for radiant will instantly void your warranty as well as damage the unit over a relatively short period of time.

    As others have noted, definitely check the numbers again what you're designing for as well for GPM required, pressure loss, output, etc.
  • Boilerpro_2
    Boilerpro_2 Member Posts: 89
    Thanks, guys,

    I haven't run a load because I haven't been back there to measure, but I can't see it being over 30,000, and likely alot less. As for code approvals, who knows. Here in Illinois there are no licensing requirements,etc. whatsover for heating contractors, so just about anything goes...prety scary!

    Boilerpro
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