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Pressuretrol Reccomendation

Hi there! I'm very glad I found this forum as you guys have been answering some questions that I've been wondering about for years!

I'm trying to make my single pipe steam system as efficient as possible. Previously my boiler had a 0-100psi gauge on it and it was nearly impossible to tell what the cut in/out pressure was. I installed a 0-5psi and found that the cut in was 1.5psi and the cut out was about 3psi.

I reduced it as much as my Honeywell pressuretrol would allow, to about 0.5psi/1.5psi. The system runs much better. I just found out I have no main vents so I will be installing some shortly. Thanks for the help!

I would like to reduce the operating pressure even further. Providing everything else is operating properly I would like to get it down to ounces of pressure. I will install a 0-15oz gauge and would like to install a new pressuretrol capable of ounces per square inch.

Here is where you guys come in! I would appreciate a recommendation for a pressuretrol that will work with low pressure residential steam systems. There seems to be so many of them! Thanks!


  • Mark N
    Mark N Member Posts: 1,090
    Installing the main vents will reduce your pressure. What size boiler do you have? What is the EDR of the attached radiation? What is the size of the mains? I use the pressuretrol that came with the boiler. My pressure remains low because the boiler is properly sized for my system and I have adequate venting. My operating pressure in under 1 oz.
  • AdmiralYoda
    AdmiralYoda Member Posts: 318
    Mark...good questions! I'm at work and will have to get back to you on the specifics but I can say that hit my pressure limit when the system is coming up to temp. We often set the thermostat back quite a bit and this will cause the boiler to cycle between the cut in/out pressures.

    When the system is maintaining a temperature it operates at about 0.5psi if memory serves.

    After I install the main vents I figured I could increase the efficiency during the above scenario when the boiler is trying to bring the house up to temp. I thought having a lower cut-in/out pressure would be a good thing.
  • Mark N
    Mark N Member Posts: 1,090
    The actual operating pressure is determined by the size of the boiler, the size of the pipes, the amount of attached radiation, the amount of venting. If the boiler is well sized for the system, the rads will condense all the steam generated, therefore the pressure remain low. Steam will move at the slightest differential in pressure. The pressure will remain low until all the vents start to close. When the vents close the pressure will quickly rise as the steam can't move. The pressuretrol then shuts down the burner. No need to generate steam as the system is completely full of steam. But because the thermostat is not satisfied the boiler will turn back on as soon as the pressuretrol reaches the cut in pressure. Then quickly reaches cut out again and over and over till the thermostat is satisfied. The best way to bring a steam system out of set back is 2 degrees at time. Let the latent heat do its thing. Then turn up the thermostat again. I learned many years ago to just leave the thermostat at one temp.
  • AdmiralYoda
    AdmiralYoda Member Posts: 318
    Thanks again Mark. I'm learning more in 1 day here than I have in the past 7 years on various other forums. Although I'm going to have to do the calculations....I have a gut feeling my boiler is over sized and setting the thermostat back as far as we have has not been helping us much.
  • Mark N
    Mark N Member Posts: 1,090
    No problem most here were steam ignorant at one time. The best investment for an owner of a steam system are Dan's books. "The Lost Art of Steam Heat" and "Greening Steam " are a necessity.
  • Fred
    Fred Member Posts: 8,513
    The pressuretrol is a safety device. If working properly, It will control your pressure so that it never goes over about 1.5 PSI. However, if the boiler is sized correctly, if the near boiler piping is correct and if the mains have the proper venting on them, you should never reach that cut-out point. Typically a properly set up system will run in the ounces unless you are trying to recover from a deep thermostat setback or it is extremely cold outside and the boiler needs to run for extended periods. Make sure those things are correct and and that you clean the pigtail (that the Pressuretrol is mounted on) at least once a year and you should be fine with the Pressuretrol you have on there. Many of us have added a Vaporstat to our boilers. Basically it serves the same function as a Pressuretrol but is "controls" pressure in ounces rater that pounds. Typically they are set to Cut-in at around 4 ounces (or anything lower) and cut out at about 12 ounces (even with deep setbacks and/or extremely cold weather. That lower pressure during those two conditions maximizes the systems ability to move and condense steam. It also leads to potentially more short cycles but that's not a bad thing on those rare occassions. We then keep the pressuretrol on the system (wired in series with the Vaporstat and the LWCO) as a "backup" safety device should the Vaporstat ever fail (the Pressuretrol should kick in at the .5PSI cut-in and 1.5PSI cut-out).
    To get that benefit, however, the vaporstat and Pressuretrols should be mounted on seperate Pigtails so that a clogged common pigtail will not disable both devices.
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