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Circulator sizing and another question...

overpop Member Posts: 52
edited August 2015 in Radiant Heating
Hi all, I ran 1200 feet of Onix 3/8. 6 loops at 200 feet all one floor. What size circulator do I need? Read Pumping Away, beginning to make sense of it as I may have to replace my oil boiler. by myself and many more questions may follow. But for now that circulator size is important. Second question: I am leaning towards the Pure Pro Trio oil but can't decide how to size it (BTUs) as I installed a Woodstock Progress Hybrid and that is a major heat source (they are amazing...( as a woodstove burner my whole life). Old boiler is 139000 btus with 3 zones of baseboard but I am overriding 1 zone of baseboard with radiant and the woodstove.
Looking forward to learning from this forum as I have many challenges ahead of me.
Thanks! Jonathan


  • Rich_49
    Rich_49 Member Posts: 2,766
    What circ would depend on what the required output , temp and flow rate for the design heat loss . 200' is not terrible but you will want low temp with any of the rubber type products . High temp is not good for longevity . Do you know these pieces of information at present ?
    What is your location and how are the walls and ceiling or roof insulated , what type of windows and doors do you have ?
    Search for Slant Fin heat loss calculator and start entering all the info , don't overlook or forget anything . We'll be here .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • hot_rod
    hot_rod Member Posts: 22,480
    about .5 gpm is all you want to try and shove thru that 3/8. At .5 pressure drop is around 7 feet for a 200 foot loop. The pressure drop curve goes up like a hockey stick from there.

    Is this in a slab, or a staple up under wood? What about floor coverings? Not uncommon to see temperatures of 150- 160 if is under wood and carpet. Hopefully you don't need to run that high, but it is rated for 180°F. Possibly your baseboard will need that temperature at design temperatures also.

    The load calc and system design will give you the info you need as far as loop temperature and flow rate.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • RobG
    RobG Member Posts: 1,850
    hot rod said:

    about .5 gpm is all you want to try and shove thru that 3/8. At .5 pressure drop is around 7 feet for a 200 foot loop. The pressure drop curve goes up like a hockey stick from there.

    I love the hockey stick analogy, I've never heard that one before.
  • overpop
    overpop Member Posts: 52
    This is staple up, wood floor above.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    The maximum you WANT to get from a floor is 30 btus/sq ft./hour. This is not a physical limitation, but rather a human physiology limitation. This equates to a floor temperature of 85 degrees F., the maximum recommended for normal foot traffic. Bathrooms are allowed to go to 90 degrees F provided contact is not long term.

    You really need to perform a heat loss calc on a room by room basis to determine true loads as Rich pointed out above. Plenty of free programs on the i-net. This will then dictate flow requirements, which then dictates pump sizing. No good short cuts that are worth pursuing in this business.

    In addition to the pressure drop of the longest small bore circuit (keep tube length the same +/- 10%) you have to add the distribution piping and components that system flow will be going through,

    It's not rocket science. It's actually harder than that :wink:

    And most of the newer boilers have more computer brain power on them than the spacecrafts that first circled the moon with humans aboard.

    Done right, you will enjoy the highest degree of comfort possible. Done wrong, you will regret the decision moving forward. Noise, air binding, component failure etc., and in 99% of those bad cases, the installer had no real "plan" in place, no loss calculation, poor heat source selection (tankless heaters are NOT a good source for space heating only) and they ignored advice given by experienced professionals.

    We are here to help.


    There was an error rendering this rich post.

  • hot_rod
    hot_rod Member Posts: 22,480
    Other important numbers once you know the BTU/sq. ft, are the required supply temperature. Plywood and wood flooring have some temperature limitations to consider. Depending on the type of wood you can get info from the various wood flooring associations.

    Excellent info at www.launstein.com regarding wood over radiant.

    Also the usage of the room and the amount and type of furnishings. The floor under couches and beds, for example does not output the same as open space flooring.

    In Modern Hydronic Design, the author suggests a maximum of 15 BTU/ square foot output with plateless staple up systems 8" on center tube spacing. He has pretty good data to support that as does Radiant Engineering in Montana, the manufacturers of transfer plates.

    With direct tube staple up, you may get striping, good temperature output directly above the tube, but much less between. So you don't end up with a consistent floor surface, or the higher output number ME referred to above.

    Sometimes what happens with plateless tube installations is the supply temperature is jacked way up to overcome the lack of lateral heat dispersion, if the system cannot maintain temperature on design days, or colder.

    Also keep an eye on humidity levels with hardwood floors. High operating temperatures and low humidity together can cause issues with the hardwood.

    So determine the load as BTU/ sq. ft for the room, then you can get a better answer.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Mark Eatherton
  • Rebe
    Rebe Member Posts: 1
    Have always used the "Little Red Schoolhouse" method to size circulators (pipe length X 1.5 X.04) to get head. Never considered the pressure drop through the boiler itself. Recently had a small hot water boiler replacement piped identical to the original, and the existing system circulator turned out to be too small due to the added resistance of the new boiler. Been looking at manufacturer's specs and don't see any reference to pressure drop or feet of head across the boiler. How do I know my circulator will be large enough to provide enough head to get through the boiler?
  • Paul48
    Paul48 Member Posts: 4,469
    Most, if not all I&O manuals cover circulator sizing. Some manufacturers make it clearer than others. Give us an example of one you can't find info on.