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Main Air Vents / Steam Thermostat

NShak Member Posts: 38
Homeowner in NJ...

Need to add at least one main air vent to each of my two steam mains.  Can anybody recommend a manufacturer and model.. Gorton vs Hoffman vs other? 

Also need to replace my thermostat w/ one rated for specifically for steam.  Any recommendations?  I'm not exactly sure that I truly understand the mechanism of a steam-specific thermostat, so any education/referral on how this works would be helpful too.

Thanks to all.


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,515
    vents and thermostat for steam

    gorton #2 gives a bigger bang for the buck than the 2.5 hoffmann #75 vents it replaces. check your vertical clearance though as they are bigger.

    don't forget that low pressures actually assist the vents in getting the air out and the steam up. while you are getting your hands dirty, why not put on a vaporstat, and a good low pressure gauge [ 0-15 oz.].

    the honeywell vision pro functions well for me. there is a setting in the menu for cycles per hour, which for steam would be 1. it has the advantage of being able to operate with 1 or 4 remote sensors, so that the main unit may be up to 100 ft. away from the sensor. sometimes it's useful to locate the sensor in a colder part of the building for quicker response  to falling temps.--nbc
  • NShak
    NShak Member Posts: 38
    Vents / Guages / Vaporstats

    How about Gorton #1?  Their website seems to indicate that either a #1 or #2 is acceptable, but not clear on which one is preferrable.  [url=]  If I only use one main vent per line this year, I'm assuming the one with the larger opening would vent the cold air out the lines faster?  Any opinions.

    Definitely need to get a better guage- will check out the gaugestore.

    Will also look into the Honeywell thermostat you recommended. 

    As for vaporstats... I don't have one now.  Any recommendations?  Can a homeowner (me) install one?  Will look into Dan's books to learn more about how they work and and how to properly use one, but if you know of any other resources that can learn from, then please let me know.

    Never too early to get ready for the upcoming winter season in NJ! 
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,515
    size matters!

    when we changed out our 1,050,000 boiler a couple of years ago because of a leaking section, we made a number of changes to the whole system:

    corrected return piping slope [water-hammer]

    installed a vaporstat and low pressure gauge [standard pressuretrol supplied with the boiler is not accurate below about 2 psi, and allowed the pressure to go up to 10 psi  when set low]!

    increased the main line venting by a factor of 5 [by 3 ounces, the vents have removed all the air, and by 8 ounces the rads are hot] my view is you can never be over-vented, however all lines should be equally over-vented to begin with. the alternative is to pay your fuel company to squeeezze the air out of constipated little openings.

    the result of these changes reduced our gas consumption by 25%, the biggest factor being the vents and the pressure. so it pays to keep these systems in tip-top shape! the vents probably paid for them selves in a month!

    do a search for "vaporstat" here. a 0-16 ounce model is best, but all we could find locally on short notice was 0-4 psi. the various models differ in how they react to a rise in pressure i.e. make or break the circuit.--nbc
  • Gorton Main Vents

    A Gorton #2 vent has almost 3 times the venting capacity of a Gorton # 1. You want lots of venting capacity on your steam mains as the faster you can get the air out of them, the faster steam gets to your radiators.

    Dan's books- Dan offers 3 of his books on steam heating  in a package called "A Steamy Deal". It's well worth the money and very quickly pays for itself. Look in the "Shop" section above. Read "We Got Steam Heat" first as it gives you a good introduction to steam heating.

    As for other`resources on steam heating  - Most of the best resources I found are located on this site.  Look around  "off the Wall"...look under the "Resources" and "Systems" labels at the top of this page.  There is lot great articles/resources located there which will help expand on what your learn from Dan's books.

    Another`site you may want to look at is Gerry Gill's.

    His website has a lot of good info on steam heating . make sure to take a look at some of his pictures on main venting setups. He is one of the super steam pros and I always read his informative comments when he posts here on the "Wall"

    - Rod
  • Patrick_North
    Patrick_North Member Posts: 249
    Vaporstat/ thermostat cycle limit interaction

    Don't mean to derail this thread- I _think_ this is still on topic...

    Can someone tell me more about how a vaporstat (which helps keep pressure low and minimizes cycling on pressure, right?) works in conjunction with the "cycle limit" settings on a thermostat. It's making my head swim a bit. does the vaporstat make the cycle setting unnecessary?


  • Unknown
    edited August 2009
    Thermostats & Vaporstats

    On the residential steam boiler there are controls for regulating the amount of steam produced and for safety.  Very simply most of these controls are "switches " on the electrical line that supplies power to the burner. If one of these "switches " is open the burner doesn't run.

    These controls sense different situations, Most residential steamboilers come with a Honeywell Pressuretrol which senses pressure. It can be set to turn off its switch when the steam pressure reaches a set pressure level and set to  turn back on when the steam pressure drops below a certain pressure level. The pressuretrol is designed for a wide variations of pressure though one of the faults of the Pressuretrol is that it isn't very sensitive/acurrate to pressure change at low operating pressures.  The Vaporstat while functionately the same as a Pressuretrol is designed to operate a very low pressure so is the preferred pressure control if you want to operate your boiler at the lowest pressure possible.

    A thermostat is just another "switch" . It senses temperature and can be set to turn off when the room it is installed in reaches a desired temperature setting.

    See Jamie's explanation of the thermostat operation below and thanks to Jamie for correcting me.
  • Jamie Hall
    Jamie Hall Member Posts: 17,185

    not exactly, on the vaporstat/thermostat cycling.  The thermostat senses temperature -- it does not have any way of knowing whether the boiler is on or off.  The old fashioned ones had an anticipator which needed to be set (a finicky job) to actually heat the thermostat up when the boiler was running, to compensate for the fact that the radiators would keep radiating long after the boiler was shut down by the thermostat.  The newer ones have a cycles per hour setting (for steam it is typically one cycle per hour) which basically limits the length of time between thermostat calls for heat, regardless of temperature.  If the temperature is low, the thermostat calls for heat -- and keeps calling until the temp. reaches the set point (or in some really fancy ones, somewhat below the set point, as the thermostat 'learns' how much overshoot there will be once it turns off, and compensates for it).

    The vaporstat, on the other hand, senses only pressure in the boiler.  If the thermostat is calling for heat, and the boiler is below the cutout point (typically around 8 to 10 ounces per square inch in residential work) the burner is turned on.  When the radiators are full of steam, assuming adequate venting, the pressure in the system will start to rise.  At the cutout, the oil burner will stop and the pressure will start to fall as the steam condenses.  When the pressure falls to the cutin point, the burner will start again and so on until the thermostat is happy.  Since the boiler is still hot, there is very little loss of efficiency due to this type of cycling.  (Note that some gas burners have a way to turn down; that's a little different).  If your venting isn't adequate, or you have crossover traps stuck closed, the pressure will start to rise before the radiators are full -- then you have problems with uneven heat (or no heat at all)!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Patrick_North
    Patrick_North Member Posts: 249
    Still scratching my head...

    So, let me talk this through- stop me if I'm missing something:

    Say a cold snap hits- the system has a long way to go to get the house up to temp. The thermostat calls for heat, and here begins cycle one. The rads fill and then slowly pressurize. At a couple of ounces, my vaporstat cuts out the burner, ensuring that I don't waste fuel- here ends cycle one. The pressure drops. Now, the moment the pressure drops below the vaporstat's cut in, I still haven't met the thermostat set temp. However, I've set my thermostat to one cycle per hour, so the boiler can't kick back on. Why the wait? There's still some nice latent heat left in those rads. Maybe in the next hour my thermostat temp will be met by the rads that are still putting off heat. If I didn't limit the cycles, maybe my thermostat would be satisfied at the very start of a cycle, meaning I'd overshoot the temp.

    Something like that?

    I guess I was fretting (initially) that it would be possible to create a situation where my system couldn't respond quick enough- where one "charge" of the radiators an hour wouldn't be enough to overcome heatloss. But in talking it through, that seems like, well, fretting...

    This stuff just fascinates the heck out of me all- thanks for sharing.

  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    All I know about steam I read here.

    I was going to title this "I know nothing about steam heating."

    But I do understand controls, especially in theory, for what that's worth.

    So Imagine your thermostat calls for heat.

    Boiler starts up.

    When the vaporstat detects that the radiators are all full, it turns off the boiler. Note that the thermostat is still calling for heat.

    So when the steam in the radiators condenses enough, the pressure goes down, the vaporstat turns on again, and the process resumes. The only way the vaporstat can affect the thermostat is by heating it up or allowing it to cool off.

    So if I understand you, your problem does not exist.
  • Patrick_North
    Patrick_North Member Posts: 249
    I'm with you, but...

    ...when you say "the process resumes," this assumes the cycle limit setting is satisfied on the thermostat. If my thermostat limits the boiler to say, one firing cycle per hour, then I need to wait- even if I'm within operating pressure.

    If for some reason the radiation was so undersized that one "charge" an hour couldn't keep up with heatloss, I guess the simple solution would be to set the cycle limit to 2.

  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666

    I think we do not understand each other. Another possibility is that I do not know how the cycles/hr mechanism of a digital thermostat really works. I have tried to find out, without success. And I have two of them in my house, both Honeywells.

    One way they could work is to vary the hysteresis (size of the dead zone), and that the numbers indicated are just approximate.

    Another way is they could count the on-off operations and arbitrarily stop (in the off position) when the count was met until the time expired. This seems a lousy way to do it.

    A third way is to run the output of the thermistor through a low pass filter and set the bandwidth to, e.g., 1 cycle/hr, 2 cycles/hr, etc. In analog days, this would be impractical, but with modern digital filters, it would be no problem at all.

    As I said, I do not actually know what goes on in those thermostats, but the third way seems the most sensible. Maybe they even do it that way. I hope someone here really knows and enlightens both of us.

    But if my guess is correct, you would be OK because the thermostat knows nothing about what your vaporstat is doing. The thermostat asked for enough heat to get the temperature up to its set point. The boiler started and filled the radiators. The vaporstat stopped the boiler when the radiators were filled. The thermostat knows nothing of this. When the vaporstat noticed the pressure drop, it turned on the boiler again. The thermostat does not know that. So more heat is delivered. The only time the thermostat gets involved in any way is as the temperature in the room crosses the set point on the thermostat.

    See, the thermostat actually knows nothing about the boiler firing cycles. All it can know is the number of heat calls it makes. There is a relationship between the two, but it is not a one to one relationship.
  • Condensing & Pressure

    A factor you have to take into consideration is that when house (outside) temperature is very cold, the radiators are condensing steam faster than it can enter the radiator and collapsing steam is producing so much vacuum that (unless your boiler is way oversized) you won't be getting much of a pressure build up so it isn't likely that the pressuretrol/vaporstat will shut of the boiler until the house is well on the way to getting warmed up.

    My impression is /was that these new thermostats work by counting the on/off cycles as in JD's second option. However since I don't know for sure (See Jamie's explanation above) and I don't want to mislead anyone, I'm now staying neutral.

    This is a really interesting subject.  You might want to read Tekmar's data sheet on the 279

    as it has some interesting explanations and graphs.

    JD- You're more articulate on this subject than I am. Maybe it might be in idea to post a question in the "Controls" section of the Wall and maybe we could get more info on this type of thermostat and how it actually works. You might outline your options as you did above and see where the discussion leads.

    - Rod
  • Jamie Hall
    Jamie Hall Member Posts: 17,185
    It can be confusing

    but only, only if you confuse the boiler, cycling on pressure with the vapourstat, with the thermostat, cycling on time and temperature.

    The Thermostat has NOTHING to do with the boiler cycling on pressure and, in fact, doesn't know anything about it.  All it does is ask two questions: is the temperature below the set point and, if so, has it been more than a certain time after the last time it turned on?  If so, the thermostat turns on AND STAYS ON regardless of what the boiler does (or doesn't) do until the set point is reached.  Period.

    The vapourstat on the boiler, meanwhile, asks only one question: is the boiler pressure less than the cutout limit?  If so, it allows the burner to run IF the thermostat is calling for heat.  The vapourstat knows NOTHING about the house temperature or cycles per hour -- all it knows and cares about is pressure.

    So let's try a scenario here: that really cold morning.  The thermostat is sitting there on the wall, and time passes.  Once it finds that it has been more than an hour after the last time it called for heat (for one cycle per hour), it wakes up and checks the temperature.  The temperature is below the set point.  The thermostat then simply closes a switch which allows power to go to the burner controls -- which include the low water cutout(s) and the vapourstat.  Assuming there's water in the boiler, the low water cutout(s) are happy.  The vapourstat checks the boiler pressure -- low, so fine and the burner starts.  Steam starts to fill the system.  After a bit -- say 10 minutes (remember, it's a cold morning) -- steam pressure starts to build and the vapourstat senses high pressure and shuts off (the thermostat is still on).  The steam condenses, and the vapourstat senses low pressure.  If the thermostat is still on -- and it probably will be; it's cold outside) -- the burner kicks on again.  And so on until the THERMOSTAT is satisfied.  Then it shuts off, and the burner shuts off.  Then you have another wait for a while until the timer times out in the thermostat, and off you go again.

    Now suppose another scenario: it's a warmish afternoon.  Time passes.  The thermostat checks the time -- it's been more than an hour since the last run, but the house is still warmer than the setpoint.  Nothing happens.  Eventually the temperature drops to the setpoint.  Now the thermostat turns on; the vapourstat checks the pressure and it's low, and the burner fires.  But it's warm out, and the house is losing heat slowly.  So, before the radiators are full and the pressure starts to rise, the THERMOSTAT is warm enough and turns off.  The burner shuts off -- long before the vapourstat even realises that the burner is firing.  Then you have another wait for a while...

    Does that help any?

    Bottom line: the thermostat plays with temperature and time.  The vapourstat plays with pressure.  The thermostat hasn't a clue about the vapourstat, and the vapourstat hasn't a clue about the thermostat -- but the burner will run ONLY if both of them say go.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Patrick_North
    Patrick_North Member Posts: 249

    Jamie, I think I have misunderstood something fundamental, here - that is, if I understood your post.

    I thought that the "cycles" the thermostat iscounting arefrom "burner on to burner off," but in your explanation it looks like the cycle in question is "thermostat call for heat to thermostat call for heat."

    That's a much simpler scenario.


  • Thanks!

    Jamie- Thanks for clearing this up. The way my boiler is wired it would appear it could be either way.

    - Rod
This discussion has been closed.