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One pipe system, radiator vents

PatrickOPatrickO Member Posts: 14
edited October 8 in Strictly Steam
I bought my first house in June. Before that my sum total knowledge of steam heat was knowing not to touch the radiators after suffering a minor burn at an aunt's house when I was 4.
About a month ago I figured with winter approaching I wanted to educate myself a bit on steam so I Googled a bit, watched a clip from Ask This Old House, and decided to replace the all the radiator vents with new ones from Home Depot. Also went around made sure all the radiator valves were fully open.

Cranked up the heat to make sure they worked and not a single vent closed. The radiators get screaming hot fairly quick. There is no water hammer anywhere. But the vents whistle when releasing the air and once the steam arrives, which is when I thought they were supposed to close, they just start steaming like a kettle and after a few minutes start spitting water.

Did I happen to get 4 faulty valves? What else might explain this? I thought that once the vents got hot, the diaphragm would push the pin up to close the vent. What could cause them to stay open?


  • Jamie HallJamie Hall Member Posts: 13,412
    Ah... oops... You might well have gotten 4 dubious, if not actually faulty, valves. Yes, they are supposed to close when steam hits them.

    Were you sure the old ones were not working? Unless they have been abused (mostly from too high a pressure) they tend to last pretty well...

    Venting single pipe steam is kind of an art, and no one gets it right the first time. It goes in steps: first, make sure that the boiler is not over exuberant. It should shut off when the pressure reaches 1.5 to 1.6 psi. You don't need more than that. There is a control on the boiler for that. Second, there should be fairly generous vents on the steam mains, so that steam is distributed as quickly and as evenly as it can be. Then you can start playing with radiator vents. The trick is to get the right vent size for each radiator, so that the heat is as you like it. In general, slower vents (assuming you have some main venting) will give better results. A lot of folks here really like the Vent-Rite #1 adjustable, because it lets you adjust the venting rate to get it right. Gorton also makes a good line of vents, but they aren't adjustable.
    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
  • dopey27177dopey27177 Member Posts: 401
    Firstly before replacing vent valves it is important to make sure the set steam pressure does not exceed 2 PSI. This maximum setting is for small buildings. The steam pressure is based on the resistance of the piping in the building. Most small buildings have a 1/2 PSI drop in pressure at the end of the steam amin.

    The pressure control setting in your case should be 1 PSI start the burner and 2 PSI shuts the burner. It does not matter whether you fire with gas, oil or propane.

    When purchasing vent valves you can save a lot of money by purchasing on the internet.

    Maid O Mist and Gorton vent valves in my opinion are the most reliable vent valves. Go on their site and you will find skematics on where to put the vent valves in relation to where the radiators are to the boiler and the thermostat.

    Other things to look at is the pitch of the radiators.
    The vent valve side of the radiator should be a little higher than the inlet side of the radiator.

    The steam main should be pitched at about 1/2" per 10 feet of linear run pipe. At the end of the steam main or where the return starts should have a large capacity vent valve , a Gorton # 1 vent will do the job. You do not need a tree with multiple vents installed. If you have a dry return the vent valve should be installed before the dry return drops to the boiler.

    What would be helpful, send us some pictures of the near boiler piping and the run of the steam main and returns.

    Attached is the Maid O Mist vent valves which for a newbe will help you balance the system with out buying additional valve when the vent valve is not suitable for that radiator.

    The Maid O Mist / Jacobus vent valve has many orifice selections which when experimenting with what is best for that radiator without having to buy a different vent valve.

    Additionally, I have enclosed a a section from my book that explains system air removal.

    The book is Steam the Perfect Fluid for heating and some of the Problems, available at Amazon and Barnes and Noble or from my stock.

    Should you wish to contact me you can email me at [email protected]


    Additionally, piper insulation on the near boiler piping and steam Main is needed to prvent large amounts of condensate from accumulating in the steam piping.

  • PatrickOPatrickO Member Posts: 14

    Thank you @Jamie Hall and @dopey27177 for the replies

    The reason I replaced the vents is because the old ones weren't shutting and they were very old so I assumed corroded/stuck.

    My pressuretrol cut-in is as low as it goes, 0.5 psi, and the differential is set to 1 so the cut-out is 1.5 psi. Those are what they were set at to begin with, I didn't change anything.

    So, there's a lot of things wrong with my NBP but my "A" measurement is over 28" so that's good. The bottom of the header is only 18" above the water line, but the riser from the header to the main is about 36" so my guess is that makes up for it. The header isn't installed according to mfg spec, it should be offset, but it is 2.5" which is spec. The riser from the header goes to a reducing tee, 2" going one way and 1.5" the other way. All of which I plan to correct but I'm not sure have much to do with vents not closing when they reach temperature?

    The radiators are pitched correctly, as are the mains and returns.

    Only 1 of the 4 risers from the main is at a 45, one is horizontal from the main for a distance before getting to a 90 ell up to the radiator, the other two are 90 straight up from the main.

    The returns are dry returns running under the supply mains until reaching the boiler, where they each have a non-functioning main vent at their elbows which then drop to boiler return, which is piped with a Hartford Loop. The returns are also copper. I am ordering a few Big Mouths and will be installing those when they arrive, insufficient venting is better than none. I don't want to go through the trouble of calculating the 'correct' amount of vents when there's so many things that need to change, anyway, and I might end up entirely changing the system to put heat in the 3rd floor.

    Right now I have 130sf of EDR being serviced by a boiler with a net output of 358sf.

    None of the pipes are insulated.

    I'm toying with the idea of re-piping it all correctly, myself, but that's a whole different story with a host of other questions I have.

    But, again, I'm wondering if the radiator vents not closing has anything to do with any of this, or what parts. Eventually I'll be correcting a lot of things before winter but I'd like to know why, if the vents spitting is usually a symptom that is accompanied with water hammer, why do I have no hammer?

    What are the potential causes of brand new vents not closing when they reach temperature? I have learned sooooo much in the last two weeks so I plan on getting better vents then the $12 ones I got at Home Depot, anyway. I have so many things wrong but only so much money and time before winter, and right now the only thing that's making the system unusable is the fact that my house turns into a sauna, literally, if I have the heat on.

    You folks are amazing, it's awe-inspiring to read all of these forum topics.
  • PatrickOPatrickO Member Posts: 14

  • mattmia2mattmia2 Member Posts: 1,872
    The escaping steam will also destroy the boiler because it will cause fresh water to keep entering the boiler to make up for the lost steam, so you have to figure that out and fix it. Are you sure the pigtail or other piping to the pressuretrol is clear so it is actually seeing the boiler pressure?

    As a side note, adding a hot water loop below the water line, possibly with a heat exchanger might be the way to heat your 3rd floor, you could likely use pex to fish that in to wherever you have chases.
  • PatrickOPatrickO Member Posts: 14
    mattmia2 said:

    Are you sure the pigtail or other piping to the pressuretrol is clear so it is actually seeing the boiler pressure?

    Good point. How can I find out?

  • PatrickOPatrickO Member Posts: 14
    Apparently I accidently deleted my comment when I tried to add the pictures to it, and I can't remember everything I wrote, so to summarize:

    Thank you for the replies!

    Radiators, mains, and returns are sloped correctly.
    Pressuretrol is set at 0.5psi cut-in and differential of 1, so 1.5psi cut-out

    I replaced the valves because the old ones did the same thing and I figured since they were probably older than my father then they were probably stuck.

    There’s a lot wrong with my NBP that I plan to correct, but I only have so much time and money before winter and right now, the only thing making the system actually unusable is that every time I put the heat on my house turns into a sauna.
  • PatrickOPatrickO Member Posts: 14

  • PatrickOPatrickO Member Posts: 14
    edited October 8

  • PatrickOPatrickO Member Posts: 14
    edited October 8

  • PatrickOPatrickO Member Posts: 14

  • Big Ed_4Big Ed_4 Member Posts: 1,433
    Insulate all the supply steam pipes the way the system was designed . My first recommendation .

    You bought the bimetal Home Depot vents . They suck ..I

    t looks like a small house . Hoffman 40's or 1A for adjusting would be a better choice . Make sure the main vents are working . Within the first 15 min they would be hot and closed. Not leaking steam .
    I have enough experience to know , that I dont know it all
  • SteamheadSteamhead Member Posts: 13,998
    The stock pigtails on those W-M SGO boilers tend to plug up easily. I like to replace them with 270° pigtails, which are less likely to clog. At the following link, the 270° pigtail is the lower one in the first illustration:

    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • PatrickOPatrickO Member Posts: 14
    @mattmia2 @Steamhead
    So I took the pigtail off and cleaned it out, also took off the pressure gauge and pressuretrol so I could clean the fittings. The fitting to the gauge was definitely clogged so that explains never getting a reading on that before. The pigtail itself was nearly totally clogged but now it's clean as a whistle.
    My Big Mouths will be here next Thursday.

    Turned the heat on to see what would happen. The boiler cut off when the gauge read 3psi. Not sure if it's just a calibration issue with the gauge or the pressuretrol isn't sensitive enough but I think I have bigger fish to fry at the moment.

    I went upstairs to find that all 4 vents were still steaming and spitting.

    I'm still confused about what causes the vents to stay open. High pressure? Wet steam? The vents get too hot to touch so they're definitely hot enough to supposed to be closed. Is the only explanation that all 4 are faulty?

    Should I take the radiator valves off to see if those are clogged or would that be irrelevant to the vents?
  • mattmia2mattmia2 Member Posts: 1,872
    It could be a lot more than 3 psi. To really get an accurate reading you need something like a 0-3psi gauge in line with the code required 0-30 psi gauge. It could be a lot more than 3 psi by the time that 0-30 gauge moves at all. Did the burner shut off because of the pressuretrol or because of the thermostat being satisfied? The fact that multiple vents don't seal makes me suspicious of them being damaged by pressure.
  • PatrickOPatrickO Member Posts: 14
    It definitely shut off on pressure, I had the thermostat at 85 and during my 'test' the temperature on thermostat went from 60 to 62.
  • Jamie HallJamie Hall Member Posts: 13,412
    @mattmia2 tossed off an important sentence: if the vents have been subjected to excessive pressure at some point, they're probably toast.
    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
  • gfrbrooklinegfrbrookline Member Posts: 631
    If they were HD vents they were toast before they were installed. As was previously mentioned install a good quality vent like Hoffman or Gorton.

    If you are near Boston I probably have 4 Hoffman 40's I can give you since I switched to Gortons.
  • nicholas bonham-carternicholas bonham-carter Member Posts: 8,193
    The pressuretrol is not really the precision instrument we take it to be, and often, when it is being adjusted downwards in pressure, the internal linkage can become disconnected, and allow the pressure to rise up much too high. A vaporstat is really a better choice for this job of pressure regulation. A good gauge will show the ounces of pressure we should all strive to attain.—NBC
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