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Use two-pipe radiator in one-pipe system?

We have one-pipe steam heating. I have a badly flaking radiator in the LR that, in addition to looking bad, doesn't heat its side of the living room adequately. (The larger of two radiators in the roon is placed alongside the bottom of the stairs to the second floor, which is where I think most of its heat goes.) Instead of stripping/repainting or covering the current radiator, I'm thinking of replacing with it with a larger one that's in better shape. I found a great-looking two-pipe radiator on Craigslist on which both the supply and venting valves are set low on the radiator. Since the supply valve appears to match the one that's on my one-pipe system, can I replace the vent valve on the two-pipe radiator with a plug and use this two-pipe radiator in our one-pipe system?

Thank you.


Arlington, MA


  • Jamie HallJamie Hall Member Posts: 6,061
    Venting valve?

    I presume you mean a valve on the outlet?  Or a trap?

    Yes, you can plug the outlet.  You will, however, have to put a regular one pipe radiator steam vent on the thing -- usually about two thirds of the way up on the end opposite the inlet.  There may be a boss cast into the radiator already for it which you can drill out and tap.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Kevin McDonoughKevin McDonough Member Posts: 6
    Thank you.

    Right, I was forgetting entirely about the vent, and will look into that.

    Thank you.

  • ChrisJChrisJ Member Posts: 7,584
    Drilling and tapping

    You'll need a 1/8" NPT pipe tap and a size Q drill bit to drill and tap for the vent.

    Whatever you do, do not use an 1/8" machine thread tap, it won't work.

    The cast iron seems to drill and tap surprisingly easy but go slow and take your time.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment

    Steam system pictures
    Central air project pictures
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