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Cast Iron Mancave Radiator Piping

kevink1955 Member Posts: 88
I found an old Cast Iron Radiator that was originaly on a Steam system, I want to use it on my Hot Water system and have a few questions. I have a few options
(1) connect to my existing MonoFlow loop (radiator would be below the loop)
(2) put it on it's own zone with a zone valve off the existing 007 pump

The real question is what tappings on the radiator for supply and return
My thoughts are being the radiator is below the loop put the supply on the bottom and the return on top, the top return would allow any air to rise as the radiator fills from the bottom. I have them both ways at work (on the same monoflow loop no less) and the ones that are bottom supply top return will self bleed, the reverse requires raising the system pressure to 28psi and cycleing the pump to rattle it out.

The other question is can the supply and return be on the same side of the radiator or should I stager them. It.s a small radiator only about 25 inches wide if that would help decide.

Would like to know before I start removing plugs that have been in the radiator for 60+ years

Thanks Kevin


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    If the sections are only connected on the bottom, it won't work. I would pressure test with air first, 30lbs.
  • Paul48
    Paul48 Member Posts: 4,469
    Got a picture of that radiator?
  • kevink1955
    kevink1955 Member Posts: 88
    Already air tested with no problem, will try to get a few pics in the next few days
  • j a_2
    j a_2 Member Posts: 1,801
    Pics would be great….Make sure you have a low water cutoff on the boiler, if not add one...
  • icesailor
    icesailor Member Posts: 7,265

    If the sections are only connected on the bottom, it won't work. I would pressure test with air first, 30lbs.

    Its my experience that it will work better if both supply and return are on the bottom. When connecting diagonally, the hot water MAY flow diagonally across the radiator with a diagonal line of hot on the top and cold on the bottom. This really happens if the flow is too high through the radiator. If you feed both at one end, only 3 or 4 sections may heat up.

    They will work far better on their own zone. Whether a circulator or a zone valve.

    In my experience.

  • icesailor
    icesailor Member Posts: 7,265
    j a said:

    Pics would be great….Make sure you have a low water cutoff on the boiler, if not add one...

    LWC's are nice, but having NO supply or return lower than the top of the boiler is a better way to protect the boiler, and feed the boiler into the bottom or so that the feed water feeds the boiler first and must them "overflow" the boiler to add water to the system. That way, you never get a dry boiler as long as the boiler fill valve is working.

    Sort of a "Hartford Loop" for a hot water boiler.


  • kevink1955
    kevink1955 Member Posts: 88
    Thanks guys, got this installed over the weekend and it works great. I would have many old plumbers rolling over in their graves if they saw it.

    Starts out as the CI radiator with the inlet piped to the bottom left and outlet on the top right, Black pipe and fittings with chrome trim plates thru the wall. The next part is what will get the old plumbers, once behind the wall the black converts to PEX (3/4 inch) with sharkbite fittings. About a 50 foot run to the boiler a couple more sharkbites then to copper to the supply manifold and Zone valve. I was a holdout on this PEX and Sharkbite thing but this saved me at least 15 sweat joints and it went in real fast. I ran it back to the boiler tiewraped to 1 by 3 running boards, never could have kept it straight any other way. Only down side I can see is the amount the PEX expands in length when it gets hot.

    I piped the boiler side like it was a baseboard loop with a purge valve, on startup I purged it and it cleared all the air. No need for the coin vent at the radiator (had to drill that plug out) or the autovent I placed in the return where it turns down to the boiler.

    IceSailor, Thanks for the heads up on pressure testing. While I did a quick pressure test on the rad when I picked it up and it held (only tested for a few min) It did have a slow leak when I gave it a longer test at home. It had what looks like a sand casting flaw in one of the sections. I pulled a vaccumn on the rad and covered the bad spot with JB Weld. I could see where some of the JB was drawn into the flaw so it's not only sealed externaly but at least part way into the casting. After 24 hour cure time I retested at 30psi with no loss in 12 hours.

    Set the thermostat for 1 cycle per hr as this thing stays hot for a long time, I love it as it is dead silent as opposed to baseboard clicking and clacking when it heats and cools. Plus it looks real cool !! Going to be doing the other one (I purchased 2) at my Sons house an a few weeks. He gets the one that already held pressure as he has a wood floor in his Mancave.