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Sizing circulators to vintage radiant system (1950's)

There are two things you need to know to size a circulator properly.

1) The pressure drop for the most difficult part of the system, usually the loop that is furthest from the pump. This will be in feet of head.

2) The volume of water you need to move with all zones on in gallons per minute.

My guess is that it will only need a small pump given that the radiant loops are ½" copper tubing; like a Taco 0010 or a Grundfos 26-64; maybe even something smaller. Just do the math.

What kind of pump is on there now? That would give you a clue.


  • Jeff_108
    Jeff_108 Member Posts: 3
    Sizing Circulator to Vintage Radiant Systems (1950's)

    Been trying to find out more information about "antique" radiant floor systems. We've recently been introduced to an old (1950's), copper radiant floor system still in good function (no leaks, etc.). G.C. has given us "as-built" drawing of radiant system and would like us to update the system (that has already been updated in 1980, boiler only). The current system now has an 80% Burnham 210,000btu boiler feeding 5 zones, 2 that have been abandoned. The radiant floor is not fed by a manifold, but with 1" copper that drop off 1/2" loops then returns back.

    We would like to update the system with a 94% boiler and zone the 3 zones with circulators.

    Here comes the "big" question!!

    How do I size the circulator(s) to this older system? I am currently at a frustrated stand still!!
  • Jeff Amich
    Jeff Amich Member Posts: 1
    sizing circulator

    Thanks alan. The total system is in copper. Do I size the circulator to the total copper in each zone?? for example; I need to over come the head loss on 549 ft of 1/2" copper, 75' of 3/4" copper, and 121' of 1" copper. Correct? Because I am coming up with 23' of head just in 1/2" copper tubing. Was I told wrong that there is 4.2 ft of head per 100' of 1/2" copper??
  • Not the total

    of all the piping, just the most extreme loop which includes the supply tubing to get to the loop, the loop itself and then the return tubing to get back to the pump.

    The 100' of ½" tubing pressure drop sounds right. Three-quarter is around 2.5' of head/100' and 1" is around 1.5' of head/100'.

    Some rules of thumb, i.e. shortcuts:

    Pressure drop - Longest run in feet. Add 50%. Times .04 . This is your head in feet.

    Dan says figure 6 feet per 100 ft of pipe.

    These figures come out larger than yours since they include an allowance for the copper fittings.

  • Circ sizing

    Alan gives great advice, here is the same in Dans own words.
    This is in the library under "Hot Tech Topics".

  • Joe Mattiello
    Joe Mattiello Member Posts: 703

    See attached circulator sizing document from the Taco radiant made easy application guide. Good stuff
    Joe Mattiello
    N. E. Regional Manger, Commercial Products
    Taco Comfort Solutions
  • heatboy_2
    heatboy_2 Member Posts: 48
    Backwards Imagineering.

    Since the system is working, why not check your delta T across it loops/manifolds, etc. If it's the desired temperature drop (wharever you feel comfortable with) and the building already heats well, size the pump the same. It was undoubtedly design around a B&G 100, so find a wet rotor with the same curve (Taco's OO service pump comes to mind).

  • Jeff_108
    Jeff_108 Member Posts: 3
    Thank you all

    Thanks to all. Very helpful information.
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