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Troubleshooting steam heating in 120-year-old 3-story home

pnm2 Member Posts: 56
edited December 2020 in Strictly Steam
Hi, I recently had a new boiler put in and I've since been troubleshooting various issues (minor radiator leaks, some radiators only partially heating, etc.) that I just hadn't paid attention to before. My research has most recently brought me to Dan Holohan's "We Got Steam Heat!: A Homeowner's Guide to Peaceful Coexistence", which I'm now halfway through and which has brought a few things to light:

-- I noticed that, just as the book suggests, the technician set the boiler to 2 psi:


Since the book says 2 is the maximum PSI you want, and since I'm only in a house (albeit a large, 3-story one), should I try lowering the PSI to optimize fuel efficiency (and potentially the speed at which steam travels)? Or is it inadvisable and potentially dangerous for a non-pro to make this adjustment? If it IS okay, how low should I try bringing it?

-- Nearly all my radiator air vents are whistling, so I'm wondering if I should try switching out the main air vents in case the current ones are clogged after all these years. I found only these two near the boiler:


Is this something I can easily do as I did with some of the radiators, so long as I shut off the boiler? Or is it dangerous for a non-pro to switch out these particular vents?

-- The new air vents I installed on some of the radiators I sized according to radiator location as the internet suggested. However, the book says the air vent size should only relate to the size of the radiator, regardless of its location. So now I want correct accordingly. Is this just a matter of eyeballing them (small, medium, large) and/or feeling out the resulting heat that is emitted, or will each radiator have specs that tell me exactly which air vent they require? If so, how do I find this out?

-- One caveat to the above is I want to reduce the heat emitted from the radiator closest to the thermometer because the other floors of the house are otherwise not getting enough heat unless I set the temperature way high. For the moment I've solved the issue by shutting off the valve to that radiator, but I'm thinking I want to just get the smallest vent for it so I can keep the valve fully open (especially since the area closest to the valve still gets hot, suggesting to me that a little steam is still getting through and I'm concerned that it otherwise won't drain out when it condenses back into water). Is this a good way to go about this?

Thanks in advance for the help!


  • Jamie Hall
    Jamie Hall Member Posts: 23,303
    On the pressure -- you can change it, but you need to know which kind of pressuretrol you have. One kind has a clear face and two scales, labelled "main" and "diff" visible. That one the main scale is the cutoff pressure, and should be set to about 1.75 and the diff scale set to 1. There are screws on the top which you can use to change that. The other kind has only one scale on the front, and is usually a sort of blue-grey box. On that one, confusingly, the scale shows the cutin pressure -- and should be set to just above .5 (don't go all the way down -- they have a dismaying habit of coming apart if you do!). Again, there is a screw on the top to adjust that scale. The cutout pressure on those will be the scale on the front plus the differential, which is set on a wheel inside the case and which -- usually -- is set to 1, which is fine.

    On the vents. Distance has very little to do with it. One concern is -- are there any vents, called main vents, on the steam pipes themselves, near the ends? There should be... and if there aren't, balancing the system can be very difficult. Otherwise, the general guidance is that you do need slightly larger vents on bigger radiators -- if you want all the heat that that radiator can provide. In general, if a space is too hot, put on a smaller vent (like that one you mention near the thermostat!). Do this first. Resist the temptation to put a larger vent on a radiator where you need more heat until you have spent some time slowing the overenthusiastic ones down.

    And notice: this is an iterative process, even if you do have main vents, as a change in one radiator will affect all the others. Patience. If you don't have main vents, it becomes something of an exercise in tail chasing...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • pnm2
    pnm2 Member Posts: 56
    Thank you, Jamie. I'll circle back if I have any followups as I continue my problem-solving. Much appreciated.
  • pnm2
    pnm2 Member Posts: 56
    As for the main vents, I did find two on the pipes coming out of the boiler. They look like they've been there forever, so I'm thinking of replacing them just to be certain I have that covered, especially since you (and the book) stress the importance of especially that particular venting in the overall health of the system.