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Steam boiler 2 stage gas valve

I have installed a heat exchanger with 4 zones on a steam boiler. The problem i am having is that the steam boiler is oversized for the water load, and client does not turn on steam boiler unless it below 10 degrees. So I’m looking to see if there is a way to install a two stage gas valve on a steam boiler that would limit the heat output of steam boiler when only the water zones are calling and when the steam boiler turn on it can go to high stage.


  • Zman
    Zman Member Posts: 7,330
    Usually that is handled by a 2 temp aqua stat that lets the boiler run at one temp for steam heat and a lower temp for domestic hot water and/or other low temp heaters.

    Converting a boiler from single stage to 2 stage is a whole different deal. What model is it?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • mikeg2015
    mikeg2015 Member Posts: 1,187
    There's usually enough mass and water volume that it's not really worth the effort and cost for 2 stage if you can make it work. Still going to be oversized even with a 30% turndown.

    Just use an aquastat with a adjustable differential and set it to a wide 30F range (150-180)