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Monoflo to Manifold Style

Hello, I have an existing monoflo heating system that is being replaced. It has cast iron radiators with monoflo tees. The main loop in 1.25" and tees off to 1/2" for each radiator. I am considering replacing this with a PEX manifold style system. What size should I feed each radiator with? 1/2"?



  • smklin
    smklin Member Posts: 69

  • Pete_y
    Pete_y Member Posts: 1
    Pex with radiators

    I'll add to this for my brother.

    Our house was damaged from Hurricane Sandy. The current heat configuration was 1 natual gas boiler with 1 heating zone. The 1.25" loop ran around the perimeter of the house just below the first floor. Off this loop 1/2" branches fed each radiator (both 1st and 2nd floor) and 1/2" return to a monoflo tee on the main loop.

    The plan is to get the 1st & 2nd floor on separate heating systems since its a two family house. We are currently looking at two condensing boilers or something high efficient. Each boiler would feed a manifold (1 per floor), and from the manifold each cast iron radiator would get its own loop using pex.

    The radiators are cast iron Sunrads, mostly recessed. The largest radiator is at least 21 sections.

    The longest run from the manifold to the radiator would be less than 70', so assume a length of 140' for the entire loop. I'm not sure what the friction loss would be but should be within limit based on the length.

    Any help or thoughts is greatly appreciated here.
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