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Sizing pump

New here need help.diy radiant. 7 loops 280feet 1/2" pex. 1900 square feet pole building insulated well 2"foam under 5"slab n perimeter.need to know what size circulating pump n expansion tank. Any advise is greatly appreciated thanks 


  • ScottSecor
    ScottSecor Member Posts: 855
    Not in my office with good software and hardware (books/charts).  Quick internet search suggest about three feet of head.  To calculate gallons per minute,  we need more information.   Heat load calculations would be a start.   Wild guess would be about one or two gallons per minute per loop.  So somewhere between 7 and 14gpm would be a starting point.

    Keep in mind that I'm assuming a low loss header (manifold) will be supplying these seven loops.   You still have to factor in getting the boiler water from the boiler to this manifold.  Sometimes we install the pump near the boiler and other times we install it remotely at the manifold.

    Others will be able to give better suggestions.

  • tparrett
    tparrett Member Posts: 6
    Boiler has pump built in.the directions say to have a primary n secondary loop.The manual directions sat to keep the boiler loop under 60feet for piping for the loop.Burnham k2 84,000 boiler.Had a heat load calculation from a place that said 44.000 btu to heat.They asked how much insulation doors windows ect, is that a heat load calculation. I'm a carpenter I only know what I read on sites like this
  • tparrett
    tparrett Member Posts: 6
    Everything 1" copper pipe manifold stainless 
  • tparrett
    tparrett Member Posts: 6
    Live in Northern Indiana looking to keep barn around 55deg
  • hot_rod
    hot_rod Member Posts: 22,121
    .5- .75 gpm per loop is common for that size and length. Is it one zone?
    If it will be zoned use a delta P circ like a Grundfos Alpha 15-55

    Expansion tank is based on system volume. I’d guess a # 30 would be adequate 

    This info should be in the design info from where you bought the components?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • tparrett
    tparrett Member Posts: 6
    1 zone
  • GroundUp
    GroundUp Member Posts: 1,907
    A Grundfos 15-58 is perfect for a system like that, but there are several others that'll work fine too if you're loyal to another brand or wish to go with a high efficiency one. You should be able to flow .6-.8 GPM per loop depending on fluid choice and temp. A #15 expansion tank is more than adequate for a low temp system of that volume, but a #30 doesn't hurt anything.
  • tparrett
    tparrett Member Posts: 6
    Thanks for the input everyone who commented. Try to get up n running before I gets to cold