Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit


tobrien02382tobrien02382 Member Posts: 3
edited October 18 in THE MAIN WALL
Hi I’m brand new so please excuse me if this is a dumb question.  Do I have to have a vacuum breaker on a TRV on a one pipe steam radiator?   I installed TRVs but they don’t have vacuumed breakers so now I’m wondering if that’s why They’re not working. 


  • ChrisJChrisJ Member Posts: 11,256
    Mixed opinions on this.
    I really don't know how much it matters but venting speed matters, a lot.

    You need the venting speed to be close to correct so that the rooms heat properly without the trv.  If you vent too fast it will always overheat trv or not.

    What are you using to control the boiler?  If it's a thermostat which one?
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • tobrien02382tobrien02382 Member Posts: 3
    An oldish Honeywell digital wall thermostat 
  • Jamie HallJamie Hall Member Posts: 13,412
    May I presume that the TRV is on the vent? With a very small number of exceptions, vents will not hold a vacuum. A closed TRV, however, will. Since it is unlikely that all the TRVs -- never mind the main vents -- will be closed at once, however, you will get air into the radiator when the system shuts down, whether there is a vacuum breaker on the vent or not. So I'm not sure, either, whether one is needed or not.
    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
  • tobrien02382tobrien02382 Member Posts: 3
    Both of your feedback has been very helpful.  I think at this point I’m going to start looking at the pressure of the boiler as it sounds the TRVs may be ok.  PS they’re working but Rads are just getting super hot while even sets on “1”.  
  • motoguy128motoguy128 Member Posts: 182
    I don;t have TRV’s on mine. They all seem to work fine. I have TRV’s on 5 Radiators out of 16 total.

    I did add a vacuum relief on the end of the Main vent antler Because Barns and Nobles don’t open under vacuum and my vapor system with its oversized 3” main dropped into vacuum so fast and hard the vents all whistled loudly.

    I agree with others the hte vent rate needs to still be fairly close to correct. So a Maid o Mist straight vent can be used. OR use the included vent which is same vent rate as a Hoffman 40, or about a 4.5 Gorton/MoM.

    However, a TRV without a vacuum relief will allow a radiator to keep heating during a call cycle to the point where it was vented to. So if it’s heated 1/2 way, it will keep heating 1/2 way. However, it should still work as the other radiators will continue heating more and more and getting proportionally more steam in the meantime. So it acts as Radiator size limiter.

    TRV’s work best upstairs and in unused rooms you want only minimal heat in, far from the thermostat.
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!