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circulator pump sizing

Kal RowKal Row Posts: 1,518Member
laing is coming out with a less expensive version of their dc vario ( – if they can get it down to $100, it makes $$$’s over the life of the system to have a pump per zone that only draws 5-10 watts!!! The pumps are permanent magnet electronically commutated motors like the ones in your computer’s hard disk – and run on 12-24v 3-30watts (imagine a pump with an ac adapter! – or a complete heating system for which a 12hr battery backup is practical) – you can get wilo stratos ECM one today but it’s a little big for a pump per zone off a radiant manifold – with the laing, and a little vertical up and down staggering, you will be able to have the pumps practically on top of each other - I got a whole bunch of jobs right now with each radiator on home run pex – just screaming for such a pump – I am soooo frustrated with how slow this technology is moving - compared to the scientific advances of the last century, we are asleep


  • Kyle_2Kyle_2 Posts: 2Member
    circulator pump sizing

    I’m thinking about taking on a major re-plumbing of my hot water heating system and I have one area where I’m in need of more education. Its a long story as to why, but basically I’m re-plumbing all of the radiators in my one story house (all accessible from basement) from a single zone, single loop diverter tee system to a home run system using 1/2” PEX tubing, giving me the ability to have multiple zones. What I’m trying to calculate is the size pump I need, also do I need one pump per zone, each with its own manifold, or can I get away with a single pump and do my zoning with actuator valves on a single manifold. Looking at some data sheets for circulator pumps, they have curves that relate head-feet to flow in GPM. So in order to properly size the pump, I need to calculate the head feet of, I think, the longest run, or the run with the most head-feet (or is it the head of all zones and runs in aggregate?). There’s probably a reference out there somewhere that allows such a calculation based on feet of baseboard, feet of supply pipe, number of 90 degree elbows, etc… I just can’t find it.

    Once I calculate that, I can find the appropriate pump(s) based on a desire flow in GPM.

    Anyone advice on how to calculate feet of head?

    Thanks. Kyle
  • ALH_4ALH_4 Posts: 1,790Member
    Circ Sizing

    Your flow requirement comes from the heat load served by that pipe, and the temperature drop you choose to design for at design conditions. (this is not necessarily the temperature drop you will always, or maybe ever, see) I prefer to use a single pump with zone valves to cut the electrical use, if possible.

    If you are determined to do this yourself, an investment in Siggy's Hydronics Design Studio would pay off with being able to play with different designs. Think of it as spending a couple hours worth of labor you would have paid a contractor to do the job.

    You can zone radiators on a diverter tee system using thermostatic radiator valves and possibly skip the re-pipe.
  • Empire_2Empire_2 Posts: 2,343Member
    Also try Belland

    You will find a program called circuit setter. Very nice and you can even buy the slide rule calculator if you like. Quick method: Longest run in feet, add 50% to that, multiply by .04 and that will give you your required head.... NOTE this is not the proper way to do it, but it will get you in the ball park. As Andrew said, you need to determine your flow requirements, and desired temp. drop. 20* is common but does not have to be depending on how you want the system to operate...

    Good Luck

    Mike T.
  • Kyle_3Kyle_3 Posts: 5Member
    re: Circ Sizing

    Thanks, I'll check it out. The re-piping is necessary because all current pipes run below ceiling level, and I'm refinishing the basement, so it has to move anyways.

  • Empire_2Empire_2 Posts: 2,343Member

  • RJ_4RJ_4 Posts: 484Member

    AT A 20 DEGREE DROP gpm can be found by dividing the heat load by 10,000. Example 79,980Btuh divided by 10,000 = 8 gpm. to figure feet of head (pressure drop), take your total length of pipe + 50% for fittings (TEL). than you need toapply to a milinch table. Chapters 3-5 in the U.A. Hydronic Heating and Cooling book will explain what your looking for. In a system with more than one circuit, figure the TEL of the longest circuit only.
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