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Pump Sizing on Hydronic Heating in Garage

So I've added a 26' x 35' attached garage onto the side of my house and I'm going to heat the floor with a Navien NHB-55 boiler. It's a single zone, primary-secondary system, with 4 equal length loops (234' each) of 1/2" oxygen barrier Pex. Navien manual suggests using a WILO Star 2 21 for the Primary loop circulator (althought another instruction they have they suggest a WILO Star S 16)?

The question I have is how do I calculate the pump requirements on the secondary side.

I have the heat loss and BTU requirements already calculated by the contractor that installed the Pex before the cement was poured, I'm just unsure how to calculate the pump requirements.



Comments

  • GroundUp
    GroundUp Member Posts: 1,495
    Pretty much any circ in production will meet those requirements. If you're getting a 21 for the boiler loop, just get another for the floor and keep it simple.
  • Atomsplitter
    Atomsplitter Member Posts: 3
    GroundUp said:

    Pretty much any circ in production will meet those requirements. If you're getting a 21 for the boiler loop, just get another for the floor and keep it simple.

    GroundUp, thanks for the reply,
    I was wondering how the flow requirement was calculated?
    Do I simply addd up all the required flows on the engineering calculation or is it more indepth than that?
  • GroundUp
    GroundUp Member Posts: 1,495
    All the flow gets added together, but head loss does not rise beyond that of the highest loop. So in your case, the final number would be 3.8ft of head at 2.14 GPM according to the calc. Pretty much any circ will provide that. More flow never hurts anything with a garage radiant system, so the larger 21 circ would likely push about .8 GPM per loop and would better utilize all the BTU your boiler has to offer for recovery purposes IMO.
  • hot_rod
    hot_rod Member Posts: 18,209
    edited October 2022
    Looks like the Star 16 is now a 17? But it seems to be a single speed.

    A Star 5 is about perfect. A Grundfos 15-58 is another good choice

    The Star 21 is a higher and steeper curve circ, the boiler must need that circ to overcome the pressure drop

    In Wilo numbers the number is shutoff head, or the max head it can develop
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • geno907
    geno907 Member Posts: 12
    My suggestion, 0018e, I’m assuming you’re going with flow setters over telestats. If you are, you can control the flow in the circulator down to 2.14 Gal/min setting.