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Radiant Loop off HWH with Heat Exchanger

Hello,

I am looking to run a small radiant loop off of a standard 80 gallon gas fired hot water heater. I am wondering my attached drawing would be a permissible design or if you foresee any issues with this potential layout.

My plan is to set the hot water heater at 180F, add an ASSE 1017 mixing valve on the domestic side and tee off the hot to a braised plate heat exchanger with a small lead free circulator pump back to the cold inlet of the HWH.

On the secondary side of the heat exchanger I plan to use a 3-way motorized mixing valve with some sort of to-be-determined controller. I omitted some critical elements from the secondary side for brevity. There will be air elimination, make up, expansion tank, etc.

Please let me know if you have any ideas!

Thanks
Brian


Comments

  • Zman
    Zman Member Posts: 7,330
    The ASSE 1017 should tie into the cold on the other side of P1 so it pulls in colder water.
    P2 needs to be on the inside of the mixed radiant loop so the flow rate in the loop stays constant no matter what position the valve is in. Be sure it is oriented "pumping away" from the expansion tank.
    I would suggest a Taco I-Series with outdoor reset for the radiant mixing valve.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Zman
    Zman Member Posts: 7,330
    How many BTUs is the water heater? If you use the Taco valve, you could prioritize the DHW by putting the boiler condensate sensor on the hot side of the water heater so it adjusts the mix when the heater temp drops too low.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Jamie Hall
    Jamie Hall Member Posts: 18,957
    Zman said:

    How many BTUs is the water heater? If you use the Taco valve, you could prioritize the DHW by putting the boiler condensate sensor on the hot side of the water heater so it adjusts the mix when the heater temp drops too low.

    That is a critical question. Another question is... is the water heater rated to be used at that temperature? And what is going to control it? 180 is way above most water heater controls.

    Further, at that temperature, you will have to be very certain of the reliability of that mixing valve.

    But regardless of the temperature, if the heat output of the water heater isn't somewhat greater than that of the slab... not going to work.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England