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Identifying Supply and Return Lines (Hot Water Radiator)

Boatster Member Posts: 10
Before I refill my system and turn on my boiler I want to install one more cast iron radiator. The room has two 1-inch black pipe stubouts capped off. Short of turning on the heat and feeling for the warmer stubout, is there any clever trick for identifying which is supply and which is return? I don't have drawings (100-year-old house) and the pipes under the floor are enclosed in a finished basement.


  • Jamie Hall
    Jamie Hall Member Posts: 22,877
    Not really... not with the pipe underneath concealed. But... with hot water it doesn't really matter which end of the radiator is which. Usually both the in and out feed into the bottom of the radiator, and equally usually there is a valve on the inlet. But it really doesn't matter, hydraulically, even if the inlet is low and the outlet high if you wanted to pipe it that way -- not does it matter much whether the valve is on the inlet or the outlet.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Boatster
    Boatster Member Posts: 10
    Thanks, Jamie. Good to know.