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Adding a small steam radiator

Kev82 Member Posts: 4
I have 3 radiators on the first floor. I would like to add a small radiator to the Family Room by using the riser going to the radiator in the Dining Room. The new radiator would be on the other side of the wall from the one in the Dining room and I can attach to the riser just below in the basement. A small radiator will not overburden the system. How should I make the connection? As an aside, the original system was a coal furnace converted to oil. I used the oil for 18 years until the cost went through the ceiling. Replaced it with a gas boiler.


  • bburd
    bburd Member Posts: 912
    edited February 2021
    Have you calculated the heat loss of the family room to size the new radiator?

    The existing pipes were sized based on the heating capacity (EDR) of the radiator(s). The takeoff, riser and steam main may have the capacity to serve both the existing and new radiators—or they may not.

    There are pipe capacity charts in Dan Holohan’s book “the lost art of steam heating”. 

    In one pipe steam, the pipes must be installed so the steam and condensate do not interfere with each other; and pitched so the condensate can drain freely back to the boiler and will not pool in the steam pipes. There are piping practices specific to steam which differ from those for hot water heat or domestic water.

    All steam carrying pipes should be black steel; schedule 40 is usual. They should be insulated with 1 inch fiberglass as a minimum.

    Piped right, the new radiator should heat well and quietly. Piped wrong, it may bang, slosh, gurgle, spit water out of the air vents, heat poorly and generally make you wish you had left it alone.

    I don’t mean to discourage you – some members of this site have even installed their own boilers, and done a better job than many contractors—but professional plumbers who are not familiar with steam frequently screw up jobs like this. The system owners end up here looking for help.

    If you want to do it yourself, there’s a lot to learn. If you don’t, try the “find a contractor” link on this site.

  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    It would be better to give the new radiator its own feed from the main. Is that not possible?
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • KC_Jones
    KC_Jones Member Posts: 5,737
    I'm going to back my question up even further.

    What issue are you having that you feel an extra radiator will solve?

    I've seen people come on here with adding radiators, replacing them, all kinds of different ideas and many times it was just a balance issue that required a venting overhaul.

    Could you fill us in a little more on the driver behind this?
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15