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Reducing valve size, One pipe steam. Banging

Project is top floor of nyc co-op. No access downstairs except basement. My plumber guy wants to reduce 1.1/4'' valve to 1''. We are replacing a 24'' x 16'x 5'' cast steam one pipe rad with a steamview runtal 24x16x 1 /4''.
The runtal has 1'' feed and will take up less place.

Its a 4th floor bathroom- top floor rad attached to a vertical 1 1/4'' riser. We are also considering adding two elbows and nipple to top of riser 6'' above floor to align new radiator closer to wall as riser is in a fixed position.
There is already some slight banging in adjacent rooms piping. This may or may not become relevant to reducing valve size?
Does anyone have words of caution before we do this?
Thanks _ john


  • Jamie Hall
    Jamie Hall Member Posts: 23,326
    The key to avoid banging in steam heat is very simple: the condensate must be able to drain freely. This means that any reduction must either be on a vertical or no more than 45 degrees off vertical, or must use an eccentric reducer. The one sort of exception is that you can reduce from horizontal to vertical with a reducing ell.

    There is a related condition: anything which is sort of horizontal must be pitched to drain. Even a very short nipple.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • KC_Jones
    KC_Jones Member Posts: 5,739
    Agree with Jamie, reduce in the vertical only. Reductions in the horizontal can be full of issues.

    I would even suggest, why not do the reduction right at the radiator. Use all 1 1/4" then put a bell reducer on the radiator with the 1 1/4" spud connected to that. This would be the solution with the absolute least issues.

    Have the calculations been done to make sure the new radiator will supply adequate heat to the space? It would be a shame to do all that work, then realize the room is cold as a result. Those panel radiators have significantly less mass and will typically heat differently from the rest of the system as a result.

    Also, very rough guestimate on the EDR of the two shows the replacement will have less EDR, which means it has less output than the current radiator. If you post a picture of the radiator we could run the exact numbers and compare to the Runtal. In my opinion the bathroom is the last place you want to be short on heat.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • dopey27177
    dopey27177 Member Posts: 887
    Before you touch anything in your apartment the piping and the radiator may belong to the coop.
    If that is the case you may inherit something that will pay for in the future or pay for now,

    like put the rad and the piping back the way it was originally installed.