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what size circulating pump

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Tom Noftle
Tom Noftle Member Posts: 16
2 - 225' loops of pex tubing. 15,000 BTU/hr

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  • Tom Noftle
    Tom Noftle Member Posts: 16
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    sizing circulator pumps

    what size circulating pump do I need to circulate from an
    on demand heater to a 5x12, 8 plate exchanger and back, 5 ft each way, 1/2 or 3/4 tubing
  • Todd_27
    Todd_27 Member Posts: 21
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    sizing

    What are you trying to connect?

    How many BTU's/hr are you trying to transfer?
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
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    Check head requirements

    Your instantaneous heater is like to be a problem for this radiant loop.

    1st They were designed for high head pressures (water pressure from the street) much higher than you are going to get from a conventional circulator. You will need something like a Taco 009 or a Grundfoss UP15-100, relatively high head, low gpm flow.

    2nd, they usually require a delta T of 15F or more before they will even fire up along with a minimum flow rate of approximately .75gpm.

    3rd, the large btu output of the burners, even on low fire rate, is likely to be several times higher your btu heat load. Excessive cycling is likely. Shortens life of your equiptment. You may need a buffer tank of some kind to smooth cycles out.

    You may want to check with the manufacturer of your heater for this application. What brand / model do you have?

    T
  • Tom Noftle
    Tom Noftle Member Posts: 16
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    the heater is a Stiebel Eltron Tempra 24 electric. the minimum flow to activate the unit is .58gpm. I'm not aware of a Delta T with this unit but I'll try to find out.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
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    I would imagine

    electric would be a different situation. I'm not familiar with electric units in this type of application.

    Just looked it up. Looks like its 2400 watts. That would be 2.4 KW. Each KW is 3412 btu's so the most you'll see from this unit would approx 8200 btu's.

    I'll try to research this more tomorrow.
  • Tom Noftle
    Tom Noftle Member Posts: 16
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    I think the tempra 24 is rated at 24kw
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