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Advice for troubleshooting an ill-performing vacuum system

I have suffered four winters with the system shown in the overview photo (photo with the numbers). It works, and heats several rooms in the house. But it does have a hard time heating every room. If I crank it to 90 on the thermostat (old round Honeywell dial type), every radiator eventually gets steam. But that's obviously no way to live. I have brought in experts to look at it before, they have all balked at it ("Well, I'm not actually the steam guy... he's on another job. Let me take some photos for him..." and they never call me back.)

The expert I called last year observed that it was a a vacuum system (which made sense in hindsight), and since it had a few leaks, the vacuum probably wasn't working too well (also made sense in hindsight). He replaced all the leaky parts and everything maybe worked a little better last winter. But nothing like night and day. I suspect the settings are wrong.

It is in the basement of a 2-story house. I attached a photo of the Vaporstat settings. I have never touched these because I, perhaps foolishly, assumed the previous owner had them set by someone competent. This Vaporstat is an old mercury-switch model, if that helps. My reading on this site and elsewhere in the Internet suggests the DIFF setting is probably wrong, but maybe this is how it is supposed to be for a vacuum system.

The other photo is of a gadget that intrigues the so-called experts who see it. It is some sort of relief vent, located up in the ceiling where the red x is in the overview photo. When the mercury switch flips and the boiler shuts off, this gizmo hisses. I have never been able to tell for sure if it is sucking air in, or venting it out, but the room never feels steamy, so venting steam seems unlikely. One expert suspected that cutting this out of the system and capping the pipe might be a good idea.

Can anyone here offer me any advice for things to try this winter? I am reasonably competent from a technical perspective and happy to run troubleshooting experiments. Also, if someone would be so helpful as to walk me through what the various pipes are in my numbered photo, I would be grateful. The blue W is where tap water comes in. Then 1 exits the boiler as steam, mostly goes up to 2, where it splits into various circuits through the house. Some condensate presumably comes down to 3. I have no idea what is going on with all the other numbered pipes. They appear to be return lines, and are probably the "under-vacuum" side of the system. But I really have no idea. Again, any education about this would be appreciated.


  • Steamhead
    Steamhead Member Posts: 16,899
    edited September 2013
    Need a different steam expert

    that looks like a Trane Vapor system, which in the coal-fired era could also run in vacuum part of the time. It's dead-simple Vapor.

    The boiler will have to be repiped though. No matter whose name is on it, it's a Dunkirk, which is very sensitive to improper piping. That copper disaster needs to go. Somewhere I have pics of a properly-piped Dunkirk, I'll post them if I can find them.

    Where are you located?

    Edit- pics attached.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Rod
    Rod Posts: 2,067
    Steam System

    Hi- While I was typing the following I saw that Steamhead had already replied to your post. He is a very experienced steam pro and is an expert on vacuum systems! 

    If you could  post a picture of one of your radiators and let us know if there is any letters or numbers on the valves/traps that are connecting to the radiators it would further help identify your system.  From your photos it is pretty obvious why you are having problems. On the positive side, vapor /vacuum systems are/were the “Cadillac” of the steam heating systems and once you get things straightened out you will have a very comfortable and efficient steam system.

    Let us know where you are located and perhaps we can recommend a steam pro near you.

    I would also recommend that you get a couple of the steam books available in the Shop section of this website. I would start with one called “We Got Steam Heat!” as it is a very good introductory to steam heating. Here is a link to it:


    The other book I would recommend is: “The Lost Art of Steam Heating”


    This book covers all aspects of steam heating and has a section on just on vacuum systems.

    All Dan’s books are written so the homeowner new to steam heating can understand them. In a few evenings of reading it will put your knowledge of steam heating light years ahead. I should mention that these books along with other good steam books are available as a package:


    As to the problems with your boiler piping here is a link to a video that will help you understand the problems:


       There is also a lot of good information in the Library and Resources section at the top of this page.  .

    - Rod
  • JStar
    JStar Member Posts: 2,752
    edited September 2013

    Second that notion on the near boiler piping. That is horrendous, and will cause a lot of wet steam, which is a vapor killer. Vapor systems need to run on dry steam and very low pressures.

    Hard to tell what type of system it is from near the boiler. The lower returns are wrong for a Trane system. The end of the steam main would be closer to the boiler than the dry returns (with check valve). But then again, it may have been so badly butchered, that the pipes were moved around.
  • Jamie Hall
    Jamie Hall Member Posts: 23,442
    One good thing...

    hang onto that vapourstat.  The mercury ones are more reliable than the newer ones.  However, that said, the differential should be less than the main setting; try setting the differential to 6 for starters (leave the main alone for the time being).  If -- and only if -- your system were really vacuum tight, the differential as is might make sense, but with newer burners... hard to justify.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • vaporvac
    vaporvac Member Posts: 1,520
    Trane VV

    Hi, I'm a homeowner with a Trane VV system. Your relief valve looks different to mine, but it may be a bit later in date. Does your system hold a vacuum ie, is the vaporstat ever showing inches? Mine still does. You have to have that to have it work as intended if it is a Trane system. It's the only vent1 When pressure is reached it closes into a mercury pot and seals itself and goes into a vacuum. Search the lit on this site...there's pretty good explanations for pumpless vacuum system. You can also search my early posts as folks really helped me understand my system when I didn't know anything. (Not that I do now!)

    Please show pics of your rad valves to see if their original with internal orifices and perhaps some pics of your rads themselves. It could be that they've been removed allowing the steam to buzz through without filling the rads.

    Sorry about that piping. It's definitely not helping.
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
  • Dave in QCA
    Dave in QCA Member Posts: 1,786
    More Information Needed

    First, I agree with everything that has been stated in earlier responses. However, I can see other possibilities that could be the culprit too.

    Do you know what the total EDR or Sq ft of your radiation is? What size is the boiler? Input, output, Net Steam BtU, and steam sq ft. Since your boiler is gas, it would be helpful to check it by clocking the meter. This will tell your whether the boiler is actually burning gas at the rate it is supposed to.

    Now, on your steam system, do you have traps on each radiator? Or is there just an elbow connecting back to the return piping.

    The gray devise that you have pictured looks like a Trane Float trap, and it could be where the entire system is venting.

    If your boiler is not sized properly for your radiation, it will cause uneven distribution of steam. If you have traps that have failed in the closed position, it will cause those radiators to heat slowly or not at all.

    There are lots of things to consider and we just need more information.

    The piping on the boiler IS horrible and should be redone if you are wanting to get this system operating properly and efficiently.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • AndyMetalGuy
    AndyMetalGuy Member Posts: 3
    Schenectady, NY

    I had login problems and must have failed to set the checkbox to alert me to replies. Sorry for he delayed response. I will post radiator photos ASAP. I am in Schenectady, NY. Nameplate on the boiler is Crown Series 982, model JS62. Had been meaning to invest in a book or two---appreciate the recommendations. It happens that I am the GE steam turbine steam chemist (and one of the metallurgists), so it makes sense that I learn and understand my own steam system.
  • AndyMetalGuy
    AndyMetalGuy Member Posts: 3

    Wow! That video Rod linked is great. I definitely need books. Very cool. Photo of the nameplate including its ratings etc. attached. All my radiators are behind grates. I will open one up for a photo session this weekend.

    Very grateful for the responses so far. It's a bummer that I paid "experts" to fix leaks in my lousy near-pipes, when I should have been paying them to plumb the thing correctly. Alas.
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