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VaporStat for Single Pipe Residential Steam Boiler, But What Range: 0 - 16 oz/in2 or 0 - 4 psi?

As a result of its recent failure to generate more than a minimum amount of heat for longer than a short period, I am in the process of cleaning-up and upgrading the single pipe steam radiator heating system (old American Standard gas boiler) in my elderly mother's 1920's two story single family home in the San Francisco area (yes, there is some steam out here!).

The system has 11 cast iron radiators (4 downstairs and 7 upstairs, two of which, in upstairs bathrooms, are smaller than the rest). (I have not yet calculated the EDR of the system, but the 9 larger radiators are 9 two-column fin ones such as that pictured in the One Pipe Steam section of Dan's A Steam Heating Primer posting in this site.)

I know that there are, or have been, a number of issues with the system, but I am addressing what I can more easily do now to get things going in the right direction. Other things, about which I may post inquires down the road, such as addressing near boiler piping and venting issues, will have to wait.

Among other things, I have so far (i) cleaned out (simmering in white vinegar) or replaced all the Hoffman air vents on the individual radiators, some adjustable, but most fixed, so they all vent well in and out; (ii) replaced the old, almost completely clogged McDonnell-Miller 47-2 (so the proper water level is now being maintained and the low water cut-off switch isn't opened and doesn't then take hours to close); and (iii) replaced the completely clogged pigtail on which the Honeywell Pressuretrol sat (so the Pressuretrol doesn't cut out and then take hours to cut back in).

Things are working much better now, though the above work has just been completed and I have not been able to do a careful watching of the entire system on an extended basis. Nonetheless, all the radiators vent air and, sooner or later, get fully hot, and the boiler cycles in a constant, though--because of the pressure gauge issue that I address next--unknown pressure range until the thermostat stops calling for heat (the Pressuretrol is set for .5 psi cut in and 1.5 psi cut out, though its accuracy is not known).

Thus, as a further upgrade, I'm next replacing the existing 0 - 30 psi pressure gauge (with vacuum range as well), which, when the boiler is stone cold, sits at about 1.5 or 2 psi, with a new one, and also getting a low range--0 - 5 psi--pressure gauge so I can better "dial in" a lower operating pressure for the system.

Finally (and the basis for this post), I am going to get a Honeywell VaporStat L408J controller to serve as the fine cut in/cut out controller, and then repurpose (as suggested on this site) the Pressuretrol to be the fail safe (though not manual reset) high pressure (say 4 or 5 psi) back-up cut-out (on a separate pigtail, of course).

But which VaporStat range should I get, the 0 - 4 psi one (the 1017) or the 0 - 16 oz/in2 (the 1009)?

Since I don't yet know if the optimal pressure range to run my mother's steam system is, say, .5 - 1.5 psi (the low end--assuming accuracy--of the Pressuretrol), or lower, say 4 oz - 14 oz, I'm torn about which VaporStat to get since the split between them is right in the middle of what the likely optimal cut-out range would be.

Any thoughts from the those here who have vastly more experience with and insight into steam systems and their controls than I (though I have learned a huge amount from reading here and listening to Dan's videos, etc., since my mother's furnace went South just before Christmas) which is the optimal one to get?

Thank you all. Nick


  • Jamie HallJamie Hall Member Posts: 12,948
    I'd be inclined to go with the 0 to 4 psi flavor. You do lose a little in accuracy and precision vs. the 16 ounce one, but it is very likely that your one pipe system will be quite happy cutting out near -- if not slightly over -- 1 psi. Which you can do with the 0 to 4, but not the 0 to 16 ounce. Either one is vastly superior in accuracy and sensitivity to the pressuretrol -- the vapourstats really are a significantly different critter.

    Another advantage of the vapourstat is that you can set the cutin pretty low, and thus lengthen the time (though probably not much) between cutout and cutin, if the boiler is cycling on pressure.

    On the pressure gauge -- you need to keep the 0 to 30 psi gauge, even though it is pretty close to useless. Your building code people in that area are somewhat narrow minded, and the insurance people even more so, and they require it. What you can do is mount your 0 to 5 psi gauge on the same pigtail as the vapourstat, and be able to see what it really thinks it's doing.
    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
  • ndelanciendelancie Member Posts: 3
    Thank you, Jamie, for your quick reply!

    Your 0 - 4 psi VaporStat suggestion makes sense--preserve the option to be a bit over 1 psi.

    I am getting (in the mail now) (i) a replacement 0 - 30 psi pressure gauge; and (ii) a new-to-the-system 0 - 5 psi gauge (that will to do the real work).

    I'm planning on mounting (i) the two gauges and the VaporStat on a branched T off one pigtail (with the low pressure one valved so that I can isolate it for testing the system at higher pressures); and (ii) the repurposed Pressuretrol by itself on another pigtail.

    I'll probably set the repurposed Pressuretrol--once I can confirm its accuracy with the new low pressure gauge--for a high pressure cut-out at 4 - 5 psi and a cut-in at the bottom of its range (.5 psi).

    My final immediate safety measure will be to replace the existing blow-straight-up 3/4" safety pressure valve on top of the boiler (of unknown release pressure or condition) with a new, 15 psi safety valve with side discharge piped (all with 3/4" pipe) over and down to the floor.

    I hope all this makes sense.

  • gfrbrooklinegfrbrookline Member Posts: 614
    @ndelancie , before you replace the vaprtorstat you need to make sure your mains are vented correctly in the basement. What size and length are your mains? Do you have main vents?

    One of the most important parts of a 1 pipe steam system is the main vent which allows the steam to distribute evenly in the basement and reach the radiators at the same time.

    Vaporstats are a great tool to stop the boiler from adding to much pressure but if you have adequate main venting the system shouldn't build pressure.

  • ethicalpaulethicalpaul Member Posts: 1,623
    I was going to write almost exactly what @gfrbrookline wrote.

    Other things, about which I may post inquires down the road, such as addressing near boiler piping and venting issues, will have to wait.

    I can understand the near boiler piping waiting, but the main venting is, in my mind, the biggest single thing any steam owner can do to make a miserable system tolerable. And the bang for the buck is off the charts.

    Is the main venting working at all (if it exists)?
    1 pipe Utica 112 in Cedar Grove, NJ, coal > oil > NG
  • ndelanciendelancie Member Posts: 3
    gfrbrookline and ethicalpaul:

    Thank you, gentlemen. In response:

    There are a number of near boiler piping and venting issues that--however important for ultimate overall improved functioning of the system--will have to wait because of what it would take to investigate or remedy them.

    In the basement, the visible steam piping--single, too short riser off boiler, short, too low header, equalizer, single vertical take-off from header to main near ceiling , and one branch off that main to radiator in room directly above basement--are all asbestos or fiberglass insulation wrapped (some of each).

    So far as I can see, there are no vents on any of that piping (although I suppose it is possible--though unlikely--that there is an air vent on the main hidden by insulation, but I hear nothing that would so indicate).

    The only vent that I can see in the basement is on a vertical pipe coming off the top of the horizontal condensate (dry) return just as it enters the basement from under the house at the elbow where the return drops to the floor on which the boiler sits and then makes it way to the Hoffman loop.

    That vent is a large, fluted, greenish cylinder of--as yet--undetermined make and vintage. It does, however, vent the return--air escaping from it can be heard, but no steam appears to escape. (Pictures can follow after the weekend for identification assistance and analysis of whether it should be replaced.)

    The main eventually runs through a foundation wall and heads into the crawl space under the rest of the house (other than the relatively small, mostly below grade basement under the rear of the house, the bulk of the house sits only about three feet above grade, and I have not yet made the excursion into that space to scope out the situation, including to see whether (i) there is any insulation on the run of this main and its branches before they go up through the floor into the house; and (ii) there are any air vents on this main or its branches.

    That's it for now on your questions.

    Because I'm trying to address as much as I can immediately, and things like better pressure measuring and control, and having a backup high pressure cut-off, are things I can do myself right now, while installing main line air vents would probably require significant plumbing work that would be beyond my capabilities, I still want to address the VaporStat issue now, and will come back to the other issues once I know more and can evaluate them.

    Thanks, Nick
  • Jamie HallJamie Hall Member Posts: 12,948
    When you do get under that crawl space (oh joy), take a real close look at the end of the steam main(s) and the related dry return(s). There may be crossover traps there rather than vents. The crossover traps are preferable -- but they do have to be working. How to tell? The steam main should be steam hot right up to them, and their inlets should be steam hot. The outlets, however, should be a good bit cooler.
    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: 306
    If you have a truly one pipe steam system here is the first test you need to do.

    On the radiator that farthest from the boiler remove the vent valve and install a o-15 psi pressure gauge. The boiler operating pressure at this junction is about 11/2 PSI. When that radiator operates with 1 PSI in it you will have the proper system operating pressure.

    Typically 11/2 to 2 psi falls into the proper operating pressure with 1/2 PSI drop back. A vaporstat with mercury switch is the most accurate.

    Why 1 PSI in the farthest radiator is steam at 215 degrees, the 215 degrees assures that you get the full edr rating in that radiator.

    All the radiators ratings for heat out put were based on 215 degree steam temperature.

    As far as the Hoffman vent valves go do not replace them.
    What you can do with adjustable vent valves is to move them to
    the radiators that are performing well.

    That job takes patience as you need to compare the results each time move the adjustable vent valves.

    As to the quick vents on the steam main mke sure they are working.

    In a normal one pipe steam system a fast working vent valve is needed. I like to use a a Gorton D vent valve because it has the same rating as the #1 vent valve, it removes 4m cubic feet of air per minute. The Gorton D vent has a 1/8" stub so you will need a reducing bushing. Try to install it 4-6" above the t connection.

    Why a Gorton D vent, it costs about 1/2 of what a Gorton # 1 vent does.

    Don't worry about the super vent valves can do. ll the vent valves vent at the same time and the all shut down when steam reaches them.

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