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pump sizing

scott337 Member Posts: 38
forget about sizing head, use a Grundfos ALPHA 15-55 pump and it finds its ideal sweetspot! Lovely! Simple! EASY!


  • Mark_133
    Mark_133 Member Posts: 1
    pump sizing

    I am sizing up an existing customer for boiler replacement. I need approx. 70,000 to heat this home. I was going to try theWilo pump system on this job but need to figure my head and flow rate to get the correct pump. I found how to figure head on the furthest zone but how do you figure total gpm. 5 -3/4" zones(3/4" @4gpm) if you muliplt that out it is over 22gpm, seems high but is that correct.
  • bill_105
    bill_105 Member Posts: 429
    22 is a bit high!

    Learn the universal hydronic formula. It's GPM = BTUH divided by Delta T times 500. Use 20 for the delta if baseboard and 10 if radiant. The 500 is the weight of one pound of water times 60 minutes. If the job is baseboard your answer is 7.
  • Todd S_17
    Todd S_17 Member Posts: 1

    Take a look at Taco's Flow Pro Website. There are two great videos that will help you out. One reviews the Hydronic Formula mentioned above, the other discusses Delta T circulators. Pretty easy to follow and free:
  • Mark Hunt_6
    Mark Hunt_6 Member Posts: 147

    8.33 x 60 x Delta T = BTU's delivered per GPM.

    8.33 is the weight of one gallon of water.

    60 seconds in one minute

    8.33 x 60 = 499.8 which is generally rounded up to 500.

    Using a 20 degree delta T, you get 500 x 20 = 10,000 btu's delivered per GPM.

    A 70,000 btu load would require 7 GPM @ a 20 degree Delta T.

    Hope this helps.

    Mark H
  • bill_105
    bill_105 Member Posts: 429
    No No No

    Go with a Taco Variable speed. Keep it on this side of the Atlantic. Forget the Danes!
  • EricAune
    EricAune Member Posts: 432

    Much better, nicer color....shouldn't we all be going "Green"?
    "If you don't like change, your going to like irrelevance even less"
  • scott337
    scott337 Member Posts: 38
    Fresno, CA is in Europe?

    not a geography major but last time I checked, Grundfos was manufactured and assembled in Fresno, CA which is in the lower 48, the good ole USA. I think Taco is cast in India and assembled in Rhode Island? India is NOT in the US.
    Go green by going Grundfos. 70% less energy consuption will save you so much money you can buy the paint color of your choice: green, purple, blue....
  • Ivan S
    Ivan S Member Posts: 4

    I didn't know that. The castings are made in India? Now, the 70% bussiness between a small Alpha and a Taco VDT - I didn't know that either. It's hometown favorites, either Rhode Island can tax the brains out of it, or it gets sent to Switzerland via Denmark. Either way, were Red Sox fans,not Yankees
  • scott337
    scott337 Member Posts: 38
    think about delta t

    place the sensor in the wrong place and you dont get optimal performance. in fact you get a nightmare.

    and dont forget, the delta t on a outdoor reset control can actually reach a point where it will suck energy from the system to meet outside air....think....know...

  • at a 20 dt you shouldn't need any more than 7 GPM here.

  • wouldn't that mean actually reducing your energy usage, rather than just getting less for practically the same electricity?
This discussion has been closed.