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Underfloor heating controls

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I have scoured the internet for info on what controls are needed for a simple underfloor hydronic system. I do not want to individually control the temperature in each zone, but I do need something that my thermostat talks to to maintain the chosen temperature. Will the thermostat control flow volume, boiler water temperature, blending or what? I am assuming that the blended water temperature is chosen and remains static as does the flow rate. I could be wrong though. So what is the control device that is connectd to my thermostat and where is it in the manifold system? Mick

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  • hot_rod
    hot_rod Member Posts: 22,263
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    Most of those tasks are controlled by the boiler, at the boiler

    The room thermostat sends a call for heat to the
    boiler

    one zone system?
    what type of boiler?
    drawing of the piping available?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mrridout
    mrridout Member Posts: 7
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    No specific piping arrangement yet. Four zones. Not really a boiler, but a tankless water heater. The lowest temperature available at the water heater is 100F and up to 120F. So you are telling me that the room temperature control has nothing to do with the manifold and its parts, but with the call for heat to the water heater? So basically I would have to have a control that turns that unit off and on. Mick
  • hot_rod
    hot_rod Member Posts: 22,263
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    Well a tankless water heater is different animal
    it us nit designed or intended to be used for Hydronics. .So it may not have the relays electrical connection for thermostats, proper safeties, etc


    It may have gave a minimum flow that a single zone found not meet?

    I’d encourage you to go with a small boiler you get out door reset, and a lot of control  functions that a system like that really needs


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Zman
    Zman Member Posts: 7,573
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    mrridout said:

    No specific piping arrangement yet. Four zones. Not really a boiler, but a tankless water heater. The lowest temperature available at the water heater is 100F and up to 120F. So you are telling me that the room temperature control has nothing to do with the manifold and its parts, but with the call for heat to the water heater? So basically I would have to have a control that turns that unit off and on. Mick

    By the time you reverse engineer a tankless water heater to do the job of a boiler, you could have bought a boiler to do the job properly. The boiler will also perform better and last longer.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • MikeL_2
    MikeL_2 Member Posts: 495
    edited August 2023
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    Zman said:
    No specific piping arrangement yet. Four zones. Not really a boiler, but a tankless water heater. The lowest temperature available at the water heater is 100F and up to 120F. So you are telling me that the room temperature control has nothing to do with the manifold and its parts, but with the call for heat to the water heater? So basically I would have to have a control that turns that unit off and on. Mick
    By the time you reverse engineer a tankless water heater to do the job of a boiler, you could have bought a boiler to do the job properly. The boiler will also perform better and last longer.
      All of that, and, eliminate the potential for Legionella infecting the potable water.
  • mrridout
    mrridout Member Posts: 7
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    The tankless is dedicated to the heating system and nothing else. I have the tankless. How much would a boiler for a 1000 sq ft house cost?
  • mrridout
    mrridout Member Posts: 7
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    What is it that makes a boiler better. I really don't know anything about them. I'm in Texas and boilers are only used in big commercial and industrial concerns.
  • mrridout
    mrridout Member Posts: 7
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    Also, in Texas, boilers must be installed by a licensed boiler tech. It must be inspected regularly by state inspectors and meet rigorous specs. All this sounds like a pain and very costly. Just the boiler would cost more than my whole system. No, I think I will stick with the tankless water heater. Now does that put me outside the reach of any other advice anyone might have?
  • mrridout
    mrridout Member Posts: 7
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    The tankless is only on when it senses water flow. Could I stop and start the pump or is it preferable to have it running all the time?
  • mrridout
    mrridout Member Posts: 7
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    I could use a thermostat to turn on and off the tankless. I don't really see that this is reverse engineering.
  • hot_rod
    hot_rod Member Posts: 22,263
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    There is radiant installed in Texas, where are you located?

    I’d be surprised if the State boiler inspector does residential inspections. They are not usually staffed for that. But it is Texas😏

    If you have a brand and model tankless in mind, call tech support and ask how to wire a heating thermostat, and how to pipe it. That way you won’t void any warranty.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream