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single pipe or 2 pipe

kensheets2 Member Posts: 36
edited August 2018 in Radiant Heating
my question is in regards to what type of piping layout for a residential (1500SF 2 story) application. I just need some opinions on whether to go with one pipe with branch piping for the individual cast iron rads or two pipe reverse. I'm using 3/4" Pex.
I was going with the two pipe but now I'm thinking it may be overkill, I understand it has better balancing, more even heating between the emitters and a lower temp drop between supply and return, which I'm assuming translates to lower operating cost.
in other words what piping is normally installed in a simple residential home.



    JUGHNE Member Posts: 8,315
    Are you converting a steam system to water?
    How about some pictures of some your radiators...both ends.
    EBEBRATT-Ed Member Posts: 9,011
    Depends on your zoning. You could do two series loops 1 for each floor...not the best.

    One pipe can be difficult to bleed but works ok. You could do two one pipe loops one for the first floor & one on the second floor.

    best would be two pipe with trv's if needed
  • kensheets2
    kensheets2 Member Posts: 36
    I'm installing from scratch. I have collected old cast iron rads for the rooms. I have computed BTU's for the room and determined rad size by the EDR for that style unit.
    The idea was to have a loop for each floor connected to a manifold at the boiler with 3/4" pex, again I was going with a double reverse but after doing some additional reading the single pipe monoflow with branches for the rads seem to be the norm.
    The question is if the 2 pipe reverse has enough benefit over the one pipe and are there any downfalls to the two pipe.
    I would prefer to only have to put one hole in my floor joist instead of two unless the 2 pipe is really that much more beneficial.

  • jumper
    jumper Member Posts: 1,622
    Single pipe monoflow is not optimal. Why not manifold to run dedicated flex to each rad? It may be what you term overkill but how much more work is it? You may be able to use smaller diameter.
  • kensheets2
    kensheets2 Member Posts: 36
    I'm not really interested in home running each rad. You say monoflow is not optimal so may I assume that's one vote for the double reverse? lol
  • hot_rod
    hot_rod Member Posts: 14,786
    If you want each radiator to receive about the same SWT, and self balance you would need to pipe reverse return, or valved home run. I'm not clear on what you mean by double reverse piping?

    A valve at each radiator would be wise to adjust flow to different sized radiators.

    In series or with diverter tees the temperature to each radiator drops, and you would need to accommodate that in the sizing of the radiator. There is quite of bit of math involved in designing a proper diverter piping layout.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Ironman
    Ironman Member Posts: 6,367
    As someone who's done a few conversions of these old systems, I'd highly recommend a homerun system with manifolds. IDK why you would even consider a monoflo system for such high end work. Monoflo systems are fraught with problems. We work on them regularly, so I speak from experience.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Jamie Hall
    Jamie Hall Member Posts: 15,852
    If it were mine to do, I'd probably go with two pipe, reverse return. Homeruns with a manifold are nice, but two pipe reverse return can do most of the same magic. Single pipe monoflow systems are tricky to get right...

    That said...

    You mentioned a concern about holes in joists. Other than the hassle of boring extra holes, it won't be problem structurally provided you keep the holes small in relation to the depth of the joist (1 inch in 6 inch joist is no problem, or proportionally in deeper joists) and provided they are located properly: try to keep them in the middle half of the length of the joist (avoid the ends or intermediate columns) and keep them in the middle quarter of the depth of the joist. And if it's two holes, keep them at least 6 diameters apart horizontally.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • jumper
    jumper Member Posts: 1,622
    >>If it were mine to do, I'd << ... and if I can get a boiler that doesn't require a circulator ...and if I can get into above ceiling space ...then I'd located distribution manifold in attic and also a vacuum expansion tank there. Gravity circulation works well that way and I'll never have to add water. Fun to dream. I'd also sell my radiator collection and use ceiling height panels. Locate them on interior walls facing windows.
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