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# Circulator Sizing

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Member Posts: 3
Trying to determine the proper circultor for a existing radiant floor for a second floor master bath and closets. Long run from the basement. . The current B&g circulator NRF 22 makes 15 feet of head and lasts about 1 season before the motor burns out. Amped out the motor and found it to be drawing about 30% over rating. My thought is that this circulator does not have near enought head for this amount of piping. Calculated about 500 -600 feet total length for the entire circuit. Can't be sure seeing as it is in the floor. Used the formula 500(run length) x1.5 x .04=30 . So would i be correct in saying i need a circulator with 30plus feet of head at least? Any thought sor comment would be greatly appreciated. Chris in chicago

• Member Posts: 7,605
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Can you sketch your system? There are other factors like number of loops and other resistance to consider.
That formula will not work for pex loops. It is nothing more than a WAG for piped systems. You will need to either use software or something like Uphoner CDAM.
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein
• Member Posts: 1,955
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500-600 feet of tubing in a single radiant loop? What size tubing? What temp water? How is the NRF-22 mounted in the system? Do you have a photo of the piping by chance? I'm not sure what could be causing the overdraw, but a larger pump is almost certainly not going to fix the problem
• Member Posts: 22,468
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A single loop 600 feet long. Usually .5 - .65 gpm for a 1/2" loop.

Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 3
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Thanks for the comments. I will get pictures and a diagram going.
• Member Posts: 3
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Also i forgot to add this is being heated with a 40gallon water heater.
• Member Posts: 7,605
edited March 2020
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If you have a single loop of 600', it would look like the attached file with your present circulator. You are running way high on the pump curve. This make the circ run inefficiently (excess heat) and cool poorly leading to premature failure.
Probably the best thing to do would be to install a delta P circ like the Taco VR1816. You may find a conventional circ with a suitable curve but I doubt it.
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein
• Member Posts: 22,468
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But back up a step and run a heat load calculation to see what you actually need to deliver to the space that the tube services.

The example that Z showed is looking to deliver 28,000 btu/hr. Is the what is needed? That is the high side of what a single 1/2 Pex loop could transfer, especially a 600 footer 😳

It could be as simple as splitting the loop if the issue is insufficient heat to the space.

A long loop like that may be running too cold at the end to transfer much heat.

It is not an ideal pump for the loop as described, but those circulator can and do take much worse misapplication abuse and last years

An air locked or blocked loop would cause excessive circ temperatures but with some flow the pump should cool itself, it is a wet rotor type of circulator
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 22,468
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These RadPad calculators are quick and easy. Suggested .6 gpm for a 1/2" loop size
600' at . 6 gpm would be about 11'

Is that NRF a 3 speed?

IF it is actually 600' of 1/2 tube? the circ is running up the curve, ideally you want to be mid curve. But a circ sized for .6 gpm at 11' will not be easy to find. Get some better data on what the circuit actually has for length and pressure drop.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 404
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@hot_rod

Is that Radpad still available somewhere in the cardboard sliderule version? Thats pretty cool.
Supply House said not available since 2011. They have a pic of it tho.
• Member Posts: 22,468
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They were at the RPA bookstore, let me check around for some. I use mine all the time.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream