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

Adding radiators to a 2-pipe-steam system with orifices

This discussion was created from comments split from: Noises follow a steam-to-water conversion.


  • Homeowner_Brian
    Homeowner_Brian Member Posts: 2
    I am a homeowner (1923 house) who also has a 2 pipe steam system with orifices (no steam traps I can see. It works well and I don't want to convert it to hot water, but want to add some new radiators (Governale cast iron baseboards). Should the new units have steam traps, or does the whole system need to be consistent with orifices? Thanks - discovered this forum and Dan Holohan's books and really getting interested in my steam system.
  • Erin Holohan Haskell
    Erin Holohan Haskell Member, Moderator, Administrator Posts: 1,642
    @Homeowner_Brian, I've created a new thread for you here so your post doesn't get lost under that article.
  • Jamie Hall
    Jamie Hall Member Posts: 16,590
    You can mix the two -- orifices in the existing system, and modern inlet valves and steam traps for the baseboards.

    That said, since you have orifices in the existing system, be sure to arrange your boiler controls so that the pressure is kept low enough. What is low enough? Oddly, it's not hard to figure out: if any of the radiators with orifices but no trap has a steam hot outlet, the pressure at the boiler is too high. You should dial back the vapourstat (I hope that's what you have) so that the orificed radiators just barely heat all the way across when the system is run for a long time (say for a ten section radiator, you'd want the first 8 or 9 sections to be nice and hot, and the last one or two might be hot at the top -- but not at the bottom).

    Be sure those baseboard units have a definite pitch towards the outlet. It doesn't have to be extreme, but it has to be therr.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Homeowner_BrianPC7060New England SteamWorksThermalJake
    JUGHNE Member Posts: 8,678
    If your system is running at a steady low pressure and you can read that on a 0-3Psi gauge, then you could size the orifice for the BB radiation.

    If you under size the opening, and need more heat it is a simple matter to drill out the copper disc. This is if you are handy with tools.

    Are you replacing CI rads with these new BB's?
  • Homeowner_Brian
    Homeowner_Brian Member Posts: 2
    Thanks Jamie and Jugne. The pressure is set at about 2psi. I will experiment with going lower. (The boiler has a 0-30psi gauge. Ten years ago when I bought the house I never saw the pressure move much, so assumed the gauge was broken and replaced it with another 0-30. Now I know I should get 0-3psi gauge.) Thanks for the suggestion about setting the pressure. I have been assuming that I should go with steam traps rather than new orifice plates for better performance. However, I guess the advantage of the orifice is that they don't require maintenance or ever need replacing.

    The new cast iron baseboards are going into a sunroom addition that someone built on my kitchen about 30 years ago. That person removed one or two cast iron radiators and installed a small split AC/heat unit. The split AC could not handle the heat loss from the sunroom glass. I am putting the cast iron baseboard around the entire perimeter - I figure that the system has the capacity because of the removed baseboards, the fact that the windows have all been replaced, and I have add insulation to the attic.
  • dopey27177
    dopey27177 Member Posts: 717
    If you need a valve with an orifice Dunham orifice valves are available from Mepco. You can adjust the orifice to the amount of steam you need to flow thru the radiator. Because you are operating at 2 psi I would install a steam trap on the radiators. If you operate at 1/2 to 3/4 psi you can leave off the steam traps. Mepco can set the orifice at the factory if you give the edr size of the radiator for your operating pressure. You may have to do a little tweeking after the install.

  • dopey27177
    dopey27177 Member Posts: 717
    Sorry about the district heating attachment it kinda snuck through when I put in the Dunham attachment.

  • New England SteamWorks
    New England SteamWorks Member Posts: 1,426
    You can go trap or office, either way (or even loop seal). But if you can use a radiator or convector instead of baseboard it would make me happier. Baseboard and steam can be problematic.
    New England SteamWorks
    Service, Installation, & Restoration of Steam Heating Systems
  • dopey27177
    dopey27177 Member Posts: 717
    Base board in a two pipe system is fine. Just be sure that the piping has reasonable pitch.
    Also be sure that the base board is piped as a two pipe system. Also 3/4" pipe can only carry 28 edr or 6700 btus.