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Steam piping confusion

Friends house. This is a 2 pipe system. Has a branch steam line that picks up 2 radiators then both the return and steam end are piped in to a hoffman f&t trap that drains into a floor drain. The main goes all the way around the house and comes back to the boiler room running parallel to the return line. At this point both lines have vents in them and both go back into the return side of the boiler. Shouldn’t the f&t trap be at this end of the line and the branch line that picks up the 2 heaters be capped and then just connect the return from the 2 heaters back to the main return line?


  • Jamie Hall
    Jamie Hall Member Posts: 23,297
    An F&T trap s probably completely unnecessary, and a distraction.

    We have a steam main. The air needs to get out of that, so there are basically two ways to do that: either a vent at the far end of it, after the last radiaator runout, or a crossover trap allowing air to get into the related dry return, but not steam. Fair enough.

    We also may have water in the steam main. Again, there are two ways to manage that: if the main is parallel flow, you need to have a drip to a wet return at the end of it. If the wet return really is -- that is, below the water line -- you don't need a trap or anything on that. If there is no matching wet return) you need a water seal -- a loop down to the floor and back up to the dry return. If the main is counterflow, you need a drip at or near the boiler.

    Now next to the steam main we have a dry return. That receives condensate and air from the radiators. That return line needs to get rid of the condensate, so if it slopes down away from the boiler, it needs a drip to the handy wet return at that end. Otherwise it needs a drip near the boiler. In either case, it needs to be very well vented -- usually at the boiler. That vent is a main vent.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England