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and another question.....

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How critical is the height placement of the Hoffman Differential loop ? "the Lost Art of Steam Heat" shows a loop with the lower part below the boiler water line.

The bottom of my loop is well ABOVE the water line--maybe 20-24 inches. What effect would this have ? (like maybe causing the problems I've been having ?)

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  • Jamie Hall
    Jamie Hall Member Posts: 23,313
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    It shouldn't

    make much, if any, difference so long as the outlet to the boiler return is sufficiently above the boiler water line that it can't back flood.  What is important is the proximity of the one and only vent (or vents on an antler) to the thing -- the closer the better.  Ideally it (or they) should be on the dry return -- which should be single at that point (that is, if you have several dry returns, they should have joined before you get to the vent) -- just before the dry return turns and drops into the differential loop.  There should be no other vents anywhere on the system -- steam mains vent into the dry returns with crossover traps.



    Differential loops typically operate at a little above 6 ounces pressure, so you will want to be using a vapourstat set to that so as to shut down the burner before the loop operates (once the loop operates, the vent will be closed).



    What problems are you having?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • turbobike
    turbobike Posts: 28
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    main vent

    Jamie....see my other post from today. Boiler is shutting off on pressure after about a minute.
  • Jamie Hall
    Jamie Hall Member Posts: 23,313
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    I just looked at it...

    My reply to it has a better guide on piping your loop, as it sounds as though you have the smaller two pipe version.



    But here are some further thoughts.  Since you did find a lot of goop, it is possible that the little hole in the connection between the two pipes at the bottom is gooped up.  Since you got it apart once, maybe you could go in there again and poke around and make sure that water can move easily from one side to the other as it should.



    A boiler cycling off on pressure after a minute or two, presumably from a cold start, is very much not right.  But that is too short an interval to be a venting problem.  Before I go off on a tangent here, can you verify that it is a minute or two after a cold start?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • turbobike
    turbobike Posts: 28
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    questions

    just to see what happens......I bumped the vaporstat up to 10 oz. It's doing roughly minute on, then minute off. And i am getting more heat to the radiators.



    obviously not a cold start
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