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in over my head!!! need help geting a pump

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by weberj62, Aug 22, 2014.

  1. weberj62

    weberj62 New Member

    Joined:
    Aug 22, 2014
    Messages:
    4
    Loc:
    mid il
    Have read some of the responses to other guys problem and thought this would be a good place to get some advice. i got in way over my head on the radiant heat install. i have 9 loops of 1/2" pex the 261',3 at 254', and 5 at 250'. some under carpet and some under hardwood. the lay out i have for this is in 8" spacing and some 10" spacing. also was running it all as one zone for a 70 degree time thru out the house.

    i have no idea how to figure the heat load. is there an easier way to figure what pump i need. i read one post were a i guy said that max. of .6 gpm per loop for 1/2 pex. he then multipled that by the number of loops and got a gmp and feet of head.

    can someone throw me a life jacket Please!

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  2. ewdudley

    ewdudley Minister of Fire

    Joined:
    Nov 17, 2009
    Messages:
    1,680
    Loc:
    Cayuga County NY
    (It's too late to wonder about dealing with heat load by choosing a pump. You can get a little more or less heat by adjusting flow rates above and below 1 gpm or so, but not much. Plus you're not going to get much over 2 gpm no matter what pump you choose.)

    Short answer, most any small pump (approx. 50-75 watt) will do the trick for you: Grundfos 15-58 three speed, Taco 008, Grundfos Alpha, Wilo Stratos, B&G Vario.

    Long answer, you're on the right track. Estimate pressure drop according to desired GPM. Check out pressure drop table in this link:

    http://www.viega.us/cps/rde/xbcr/en-us/TD-PF_1113_(ViegaPEX_Ultra).pdf

    Table only goes down to 1 gpm, your pressure drop would be less than half for 0.6 gpm. (Multiply by 2.31 to convert psi to feet of head.) So in this example it would be 4 psi pressure drop at 1 gpm for 250 foot loops equals 9.23 feet of head.

    Multiply gpm times number of loops, so 9 gpm and 9.23 feet of head. Then look up 9 gpm and 9 some odd feet of head on the pump curve graph for the candidate pump. If point falls inside the curve and reasonably close to the curve then the pump is a good match. (Which I believe would be the case for all the pumps mentioned above.)

    If 0.6 gpm is what you want, then a variable speed pump (15-58 three speed, Alpha, Stratos, or Vario) would let you adjust flow down to your requirement.
    Last edited: Aug 22, 2014
  3. Bob Rohr

    Bob Rohr Minister of Fire

    Joined:
    Jan 9, 2008
    Messages:
    769
    Loc:
    SW Missouri

    Are you adding zone control actuators to the various loops? If so get one of the smart pumps which adjust to the system demands.

    Even without zone actuators this would be an excellent pump choice. Priced a bit higher but well worth the addition 60 bucks or so.

  4. ewdudley

    ewdudley Minister of Fire

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    1,680
    Loc:
    Cayuga County NY
    Agreed, for quick and dirty 15-58 or 008 would be fine, but if you think you may be doing separate zone controls and/or you want to save some electricity over the long haul then constant pressure pumps like Bell & Gossett Auto, Wilo Stratos, or Grundfos Alpha would be a better choice.
  5. arbutus

    arbutus Feeling the Heat

    Joined:
    Oct 16, 2007
    Messages:
    272
    Loc:
    Michigan UP
    I have five loops of half inch pex a little longer than yours, average length of 300', but equalized at the manifold to the longest length of 350.
    A Grundfos Alpha is blissfully pumping away, on low speed, moving about 2 gallons per minute, or an average of 0.4 gpm per loop.

    Whether or not this will be effective for your heat load is entirely up to the emitter, floor R value, and spacing.
  6. weberj62

    weberj62 New Member

    Joined:
    Aug 22, 2014
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    Loc:
    mid il
    thanks for the help think i am going with the alpha.
  7. weberj62

    weberj62 New Member

    Joined:
    Aug 22, 2014
    Messages:
    4
    Loc:
    mid il
    now i have the second question.

    i am looking for a pump that pumps from my boiler to the plate exchanger in the house. have one inch supply and return that are 150' long. look at some advice for this. the guy that was building this will not answer his phone so i am looking for all the help i can get. i think he was talking about a b&g nrf 36 but was wondering if the grundfos ups26-99fc 3 speed would work in this situation. just that i am going with one might as well have another one from the same company. any ideas are would be helpfull. thanks again for the above thoughts.
  8. arbutus

    arbutus Feeling the Heat

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    Loc:
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    What size is the plate heat exchanger? X" by Y" and how many plates?
  9. weberj62

    weberj62 New Member

    Joined:
    Aug 22, 2014
    Messages:
    4
    Loc:
    mid il
    it is 5 x 12 30 plate 200 to 275 btu.

    also forgot 38" ss side are with the enhanced fins 1" in and out puts.
  10. arbutus

    arbutus Feeling the Heat

    Joined:
    Oct 16, 2007
    Messages:
    272
    Loc:
    Michigan UP
    The GEA flatplate calculator (free online) for a 5x12x36 plate says about 1 psi pressure drop for 10 gpm. About right for a 20 degree differential and 100k btu/hr load.
    300 feet of 1" pex at 10 gpm, Google brought up the Uponor chart that shows 6psi per 100 feet of 1" pex at 10 gpm. 18 psi for piping, 1 psi for flat plate hx, 1psi ? for side arm, add 10% for fittings and you are in the neighborhood of 22 psi loss, or about 50 ' head. It doesn't look like either pump can supply 10 gpm at that head.

    Maybe you can cut flow in half and go to a 40 degree differential. Maybe you only need 50,000 btu/hr to start with. If you want to select a pump and be confident it will work, you do need to know the anticipated load. The Uponor Complete Design Assistance Manual walks the reader through the calcs. The Zurn radiant manual does also. Both are free online.
    ewdudley likes this.

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