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Boiler fired tankless DHW heater

Bill H.
Bill H. Member Posts: 30
New to this, so please excuse if this is a dumb question. Is it possible to have a wall-mounted tankless DHW heater that receives its heating source from a gas-fired hydronic boiler? I am considering a Weil-Mclain CGi unit, but they only offer indirect tanks for DHW. If the ansewr to my question is yes, any recommendations would be appreciated.  Thanks


  • Larry Weingarten
    Larry Weingarten Member Posts: 3,338

    I admit:  I'm confused.  Why preheat a tankless heater from a boiler?  Regardless, there is a problem I understand with the idea and it's gas fired tankless heaters have difficulty accepting preheated water.  They cannot modulate way down so as to do only a little heating.

    What are you trying to get done? 

    Yours  Larry
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
    Larry I think he is asking

    If there is a wall hung tankless unit that is heated by the boiler water. As far as I know the answer is no. There are reverse indirect heaters that heat the domestic through the coil and the boiler water circulates through the tank side. This helps with short cycling of the boiler I am told. Still not a wall hung unit though.
    Cost is what you spend , value is what you get.

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  • Gordan
    Gordan Member Posts: 891
    Couldn't he just use a FPHX?

    And mount it on a wall, if that's what he wants to do...
  • Ironman
    Ironman Member Posts: 7,379

    He's trying to save space, why not use a Buderus or Viessman Indirect with the boiler stacked on top of the tank. He'd have a better boiler in the process (MHO).
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • icesailor
    icesailor Member Posts: 7,265
    Boiler fired tankless:

    I think he is asking about a flat plate tankless. A lot are made. You mount it anywhere and pipe the boiler on one side and the DW on the other. I never installed one but didn't EF System 2000 oil boilers use them because they didn't have an internal tankless? I always considered them external tankless's.

    They have been around for years and I know that Veissmann has one among others. I seem to remember seeing one on a boiler at the Veissmann school I went to last month.
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