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Choosing primary circulator for efficiency

Hi guys,

Probably a shockingly simple question. Given a standard cast iron boiler, say 100,000 btu, and a primary loop flow of about 10 gpm, am I right in thinking the head loss will be small, like 1-2 feet? If so, how do you choose a primary circulator for that range, that is still somewhat efficient. It's easy to find a pump that will supply that, but they all seem to be at the right hand side of the curve, which if I understand isn't terribly efficient. What am I missing?



  • Brad White_9
    Brad White_9 Member Posts: 2,440
    When you include

    your air separator, tees with instrumentation, a few fittings and several feet of pipe plus the boiler, you may be a bit higher but I would say 4 feet, maybe 5 feet. A Grundfos 15-58FC with or without the check valve is right about there at speed 2. Not optimum but the duty must be met. I would not lose sleep over it.

    The boiler is the biggest variable though. (Ever pipe through a Gasmaster?) Get the best data on that part you can. Not like a Burnham Series 2 (almost immeasureable), ModCons have to be at least a couple of feet depending on manufacturer. Not sure what is available out there for finite data though.
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