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Wet or dry return?

I've been trying to learn more about the heating system in a 2 story, 2 family house just purchased. It's a typical northeastern woodframe built in the 1920s.

From what i can tell, it's a single pipe radiated system for the 2 top floors with a hydronic loop going to cast iron baseboard in the basement.

This forum (and YouTube) have been incredibly helpful in explaining the basics of this type of heating system but i still have a few questions... apologies if these are obvious or basic..

1 - do i have a wet return or dry? The return pipe runs along the side of the basement above the water line but then suddenly dips below before turning up again to meet the hartford loop/equalizer. I'm not clear on this setup

2 - as far as i can see (it's a finished basement), there is no main vent. Is this a problem? There are 2 bathrooms on the upper floors that have a 2+ inch diameter cast iron vertical heating pipe with a "bullet" style vent at the top of them. Would this count as a main vent or does it always need to be directly attached to the header at the boiler?

3 - the hydronic heating loop is 'turned on' by a janky looking switch which turns on a water circulator. Would this switch be what needs to be wired to a thermostat for the basement or should it always be on (the circulator)? I understand that the heat is either on or off and there are no zones as such. Just trying to figure out what to wire the basement thermostat to.

See photos and thanks for all the expert help!!


  • Justin20
    Justin20 Member Posts: 28
    One more photo of the return setup:

  • Jamie Hall
    Jamie Hall Member Posts: 23,323
    The "return" could either be regarded as a return -- or as a continuation of the steam main. Which it is depends on how -- if at all -- it is separated from the steam main. If it is a continuation of the steam main, it really isn't a problem. If it is in some way separated -- cross over trap, water loop seal, then it may be classed as a dry return -- but if it is close to the water line, it could give issues from water loss in the boiler or water hammer.

    The bullet vents on top of the risers are probably acting as main vents. This is OK -- a little unusual, but quite OK -- provided they are big enough. The only really reliable way to determine that is two tests: first, do all the radiators start to get steam more or less at the same time? And at least until all the radiators are filled, does the system run at low pressure (only a few ounces)? The first is easy enough to tell, but for the latter you'd need a low pressure gauge.

    That switch could be replaced with a thermostat -- but chances are that that's 120 VAC line current, so if you do go to replace it (and why not?) you'd need a thermostat rated for line voltage -- and be sure to turn the power off if you decide to work on it!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England