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Radiator thermostatic trap question

zoomzoom Posts: 68Member
I am hoping someone on this forum can share an opinion on the following for a two pipe, low pressure, residential steam system....

For one basement radiator mounted on the basement ceiling, the radiator has been enclosed in sheet metal so that the heat passes through a floor register to the kitchen above. Who ever did the metal work also enclosed the radiator thermostatic trap to the dry return, so the trap gets very hot when the radiator is hot.

Given the principles behind how a thermostatic trap works, will the trap work effectively surrounded by very hot air?

I can not see the trap (only feel it by sticking my arm through the heat register) so I don't know the make and model. However, most of the other basement traps have been Barnes & Jones T122s.


  • delta Tdelta T Posts: 789Member
    This is a good question, my gut feeling is that it will not affect it because I feel like the air will not get hot enough, but @Sailah would know
  • Jamie HallJamie Hall Posts: 11,466Member
    I doubt very much if it could get hot enough to close from the hot air. The worst that could happen is that it would close, and be slow to reopen.
    Br. Jamie, osb

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

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • SailahSailah Posts: 810Member
    A thermostatic trap operates with a 10-20 degree subcooling effect so that it can drain accumulated condensate. So if you somehow heated the trap body past 212 degrees, and held it there, then the trap would never open.

    Worst case scenario it will be a little slow to drain. But I don't think it would probably get hot enough in the metal box to affect it.

    Other question is the trap upright like it would be on radiator and not on its side? That would make trap not work right.
    Peter Owens
  • zoomzoom Posts: 68Member
    thanks everyone for their advice, seems like the consensus is that the trap should work, although with the risk of possibly suboptimal performance. And the trap is the right way up.

    Which leads me to a different questions for a different trap. For a radiator trap it makes sense that the trap is situated above the dry return so that the water can drain via gravity. Is this true also for a crossover trap? I have one crossover trap that has been placed right up against the basement ceiling so that it is just above the dry return. However, the trap is completely inaccessible and there is no way that the lid could be unscrewed and the cage unit inspected. If a crossover trap facilitates only the expulsion of air from mains, could it be situated below the dry return that it is piped into?
  • EBEBRATT-EdEBEBRATT-Ed Posts: 6,116Member
    Crossover traps only vent air...there used in place of an air vent for the steam mains It cannot be located below the dry return.

    If the trap ever fails I would remove it and install unions in the trap piping inlet & outlet connections. Put the unions in an accesable location so you can remove the trap and it's associated piping as an assembly in the future for ease of service.

    With a cold system start the boiler. The steam main and the trap inlet should get hot and downstream of the trap should stay at a lower temperature. Traps usually but not always fail open so if downstream of the trap gets hot at the same time as the main and trap inlet the trap has failed
  • zoomzoom Posts: 68Member
    Thank you EBEBRATT-Ed ... I will go with the unions idea.
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