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Time Sensitive Question About Vaporstat mounting location

sreja Member Posts: 175
Hey guys, I have a quick and sort of time sensitive question since the installer is working on this now..

We are installing new vaporstats, and they are putting them on a loop that ends far below the waterline.

I understand that the loop serves the same purpose as a pigtail, so that's not my concern -- my concern is that the vaporstats and so far below the waterline when everyone seems to be saying they should be mounted well above the waterline.

Installer insists it won't make a difference.  I worry about our dirty boiler water (it's not very clear) will be cutting life of vaporstats if they are constantly "under water", so to speak.

Photo attached showing the PROPOSED NEW LOCATION of vaporstat.

Would appreciate any quick advice and what i should tell installer to explain why it's important that they be above waterline -- iff in fact that is your understanding.  Or maybe i am misunderstanding something?


  • Mike Kusiak_2
    Mike Kusiak_2 Member Posts: 604
    It will make a difference

    If the vaporstat is mounted below the water line, the weight of the water above the vaporstat height will add to the steam pressure, making the pressure calibration inaccurate. 28" of water will add a pressure of 1 PSI.
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,394
    There's that,

    and I think that pipe will fill with crud in about 10 minutes. 
    Retired and loving it.
  • sreja
    sreja Member Posts: 175
    re: Time Sensitive Question About Vaporstat mounting location

    Whoa -- a reply from Dan the man himself!!! Dan your books are amazing!!

    As i have discussed with others, you have created a steam virus that gets into our heads here and never lets us go.

    And thank you guys for such a fast reply.  Quick clarification though:

    In all fairness to installer, regarding the water pressure -- as you can see from the photo, the pipe leaving the boiler and beginning it's downward loop to the vaporstats starts just at the top of the sight glass, and so is just at or above the high water line, and well above the normal running water line.

    So the pipe leaving the boiler to the pressuretrols and vaporstats may be considered to leave above the waterline -- that should solve the weight of the water issue.

    If so, the only real issue is the fact that the pipes to the pressuretrols and vaporstats just loop down and never up again above that original connection to the boiler, and so will remain filled with (dirty?) water right up to the very top of the diaphram etc. and wont have a gap of air with water draining back into the boiler.

    Do you still think that's enough of a problem to insist on it being repiped?
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,394

    Once the pipe fills with the water, the weight of the water will affect what the control feels. A column of water 1-3/4" high experts one ounce of pressure. I'd rather see it above the waterline. 
    Retired and loving it.
  • Mike Kusiak_2
    Mike Kusiak_2 Member Posts: 604
    Water pressure

    Even though the boiler connection is at or above the water line, the piping will still fill with water, so unless the vaporstat is mounted above the boiler connection, the column of water in the piping will still add to the steam pressure. The vaporstat must be mounted higher than the connection to the boiler.
  • clammy
    clammy Member Posts: 2,983
    raise them up

    Do your self a favor remove the pressure gauge and install a plug there and raise the whole thing up and add another cross tee then some 3/4 or 1/2  x 1/4 tees .When adding more then 1 pressure troll or vaporstat i usually raise them above the top of the boiler higher is dryer and the cross tees make it easy to brush and lean out the piping .Down low like that i will fill up with crap and not function correctly.Just wondering why so many usually on a commerical  2 stage i have 3 including the maunal reset just wondering .Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • sreja
    sreja Member Posts: 175
    Re: Time Sensitive Question About Vaporstat mounting location

    Thanks everyone for the advice!

    We re-piped it higher up and it looks beautiful now.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,575
    multiple pressuretrols

    clammy, he has the mod-u-pac, i mentioned to you:  with 3 stages of firing:50%, 75%, and 100%--nbc
  • sreja
    sreja Member Posts: 175
    edited March 2011
    re:Time Sensitive Question About Vaporstat mounting location

    Here's a picture of the re-piping with the two new vaporstats replacing two of our old pressuretrols.  I'm quite happy with it.  It's hard to see but we attached some shelf angle supports copying nbc on this forum, to support the weight.

    Everything is well above waterline, and there is a water trap in the pipe which dips down and then back up playing same role as pigtail.


    For the curious:

    Low pressure guage and 30psi gauge, two 0-4psi vaporstats for the 50% and 75% firing rate switches, one 0-15 psi pressuretrols serving as main pressure control on off, and one 0-15 psi pressuretrol with manual reset to make sure pressure never exceeds max pressure.

    Right now it's set to something like this:

    100% gas till it hits 1.6 psi

    75% gas from 1.6 to 2.0 psi

    50% gas from 2.0 to 3.0 psi

    shut off at 3psi

    In reality it never reaches its 3psi operation shutdown, because when it cuts to 50% it slowly coasts up from 2 to 2.5 and then back down on its own, cycling between 75% and 50% gas.  and that's on a warm day.  on a cold day it may never get much higher than 2psi.

    It remains to be seen if the system really gets enough heat with these settings when the weather gets truly cold -- if not we may have to bump up the pressures a little bit.  I know in an ideal world we'd run it below 2psi but my preliminary testing when we had the pressuretrols was that it wasn't sufficient.  I will try again with the vaporstats next winter.


    This completes basically the final stage of upgrading of the 14unit building's steam heating system performed over the last few years.  Controller is now a tekmar 279 with 2 indoor sensors, and there are TRVs and new traps on every radiator.  The system purs like a kitten.

    A huge thank you to Dan and his fantastic books, and the amazing and helpful community here on the wall.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,575
    now that you have some vaporstats....

    try to get those operating pressures down to the ounces range, and see what the difference is.--nbc
  • sreja
    sreja Member Posts: 175
    re: Time Sensitive Question About Vaporstat mounting location

    i shall try nicholas -- and thank *you* for all of your help on this forum over the years.

    it may need to wait for the real test until next winter though, since the loads are pretty low right now with the mild temperatures.

    The one piece of the puzzle that also might get in the way of running at low pressure (or might not) is the venting situation on this two-pipe condensate pump return system.

    I've written posts about it in this section before -- i just don't have a good feel for whether the open air condensate return means we don't need other main vents or not.

    But i shall try -- as the system seems to be working really well these days.
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