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# Pump size

Member Posts: 6
I am trying to determine the pump size for a joist bay radiant system
Total btus needed is 22000btu
Total loops 5 equal size
Pex size 1/2”
Longest loop is 250 feet including supply and return

• Member Posts: 7,339
That's 4.4 gpm at a 10* delta T and about 3.5 ft. of head. I'd use a Grundfos ups15-58 on low speed.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 6
Thanks Ironman, can you tell me what fourmula you use to calculate the 3.5 ft of head? I seem to be coming up with much more.
• Member Posts: 7,339

You can expect about .75 gpm per loop X 5 = 3.75, call it 4 gpm. It still puts you on low speed with a ups15-58.

The head calc is from the attached chart:

Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 6
Thank you, at least I know I’m not going crazy.
it’s funny, I talked to a few guys at the supply house and each one recommended a different pump, one recommend the same pump you did and one recommended the taco 007 or 008 but looking at the curve charts each one is amazingly different. I think listening to them makes me second guess everything
• Member Posts: 7,339
The 15-58 covers both the 007 and 008 depending which speed is used.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 6
Thanks for the help Ironman!
• Member Posts: 545

Dave H
Dave H
• Member Posts: 7,339
Dave H said:

Dave H

A very valid point.

Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 884
OP, You only mention the longest loop length, how close in length are the other loops to that?
• Member Posts: 6
I made a point to make each loop very close to the same length.
With all the very different opinions on the head I’m still conserend about the pump what pump to use.
When I calculate the head accounting for fittings and valves I come up with about 15, that sounds high to me.
The last thing I want is a to small or oversized pump.
• Member Posts: 7,339
Unless you've got a completely crazy piping arrangement, I can assure you that a 15-58 or a 008 will be more than sufficient. I've got jobs with 14 250' loops and one 15-58 on medium speed is pumping them just fine.

You're over-thinking this.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 6
Over thinking is what I do, I appreciate your assurance, with that, I will use 15-58, the 15-58 based on my original calculations is what I decided, until others at the supply house started adding their opinion.
Thanks again !