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Circulator definitions

Glen Member Posts: 855
A colleague and I are the discussing the merits of some hydronic heating definitions; to be specific "low head and high head" as it applies to circulators used in closed systems. We have looked at a few resources (Siggy, et al) and the terms seem to be in use but relative to pump curve characteristics and not to a specific foot head. So the question is: "are the terms still relative, and can they still be defined as below 12 fthd (low head) and above 12 fthd (high head)?"


  • Empire_2
    Empire_2 Member Posts: 2,343
    Good Q:? I personally refer to hi head as something with the "HV" designation and it would also depend on what flow @ hi head........
  • SWEI
    SWEI Member Posts: 7,356
    edited June 2015
    Depends entirely on the size of the system IME.

    We design most residential systems to have 6 feet or less of head. It's easy to do, doesn't add significantly to the materials cost, and typically halves the lifetime pumping costs. A multi-story commercial building with less than 30 feet could also be 'low head' in my book.

    A better way to view this would be as distribution efficiency. Well-designed systems are capable of moving 3,000 BTU (or more) per hour for every Watt of pumping power they consume. This is covered in some detail by Idronics 16 (starting on page 50.)
  • hot_rod
    hot_rod Member Posts: 16,872
    I don't know that there is an "industry standard" or definition for what is a high, medium, or low head circ. If that is what you are asking?

    I have alway considered the typical 15-42 or 15-58 Grundfos, Taco 005 and 007, Wilo Star 16, B&G Series 100 & NRF 22 Armstrong SL series, etc as low head.

    Taco 0011, Grundfos 26-96 or 26-99 as high head. And there are choices in between those pump spec these days, maybe medium head :smile: .

    Not to forget variable speed circulators which can cover a wide range of conditions, the Magnas from Grundfos for example can be programed to cover a very wide operating range.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Steve Thompson (Taco)
    Steve Thompson (Taco) Member Posts: 203
    Glenn - you raise an interesting question. I agree with SWEI's response (commercial less than 30' low head).

    My take on high vs low head circs is more about flat vs steep pump and/or system curves (high head vs low head systems). I don't know what you would get if you asked a pump supplier for a low head circ (how low is low?). Best bet is to pick the circ to match the application and if known, the system curve as best as possible. Low friction loss systems (baseboard, gravity conversion jobs etc.) would be considered low head. Infloor, with lots of tubing (and subsequent "lots of" friction loss) would require high head circs.

    If the friction changes dramatically with flow (typical of European systems), probably best to pick a circ with a steep curve, assuming it's a variable flow application. Typical US systems typically have flatter system curves hence are more suitable for flatter "low head" (less than say 8') circs...