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Need help- hydronic system with cast iron radiators

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cd80
cd80 Posts: 1
in THE MAIN WALL

I am trying to install a hydronic system on a single story 1100 sqft ranch style house. I have a heatmaster MF5000 outside stove and old cast iron radiators of varying sizes that are likely overkill (but what I could find used). I need to install 6 radiators that I would like to have set up on 2 zones or have individual valves on each radiator (preferably). Currently have a single circulator pump mounted on the stove but willing to change that. Thanks

Comments

  • hot_rod
    hot_rod Posts: 28,329

    that seems like a large stove for1100 sq ft it may idle a lot. Any other buildings going to be added?

    I think those are all unpressurized type stoves, some installers add a plate heat exchanger to make the home loop pressurized

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GGross
  • hot_rod
    hot_rod Posts: 28,329

    is this a job you are going to pipe yourself? Here is an example that includes a backup boiler. One pump and two zone valves is a way to get 2 zones. The red line to the right of the pic is where two zone valves would pipe in.

    Screenshot 2026-09-29 at 10.49.57 AM.png
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Ironman
  • Ironman
    Ironman Posts: 7,951

    Don’t let any of the outdoor wood boiler people convince you that you can connect the house system directly to the ODWB. You need to separate the house from the ODWB using a heat exchanger as hot rod has shown.

    You will have several long term issues if you try to short cut this, not the least of which will be oxygenated water which will rot the radiators.

    Think about it: if houses could run unpressurized systems, then why has this industry been requiring it for well over 100 years?

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • GGross
    GGross Posts: 2,060
    edited 6:14PM

    That wood boiler can heat a small neighborhood of houses that size. If it were me i would look to selling that thing and using the money to pay for a small gas unit and several years worth of fuel personally. I could take care of my heating bills plus the cost of a DIY boiler for around 6-10 years for just the cost of that boiler and my house is about twice that size in a cold climate, zone 6, just a thought..

  • hot_rod
    hot_rod Posts: 28,329

    Here is what your piping might look like. Find the plate heat exchangers at most wood boiler suppliers.

    Screenshot 2026-09-29 at 12.10.46 PM.png

    If you do tie in a back up boiler,here is a piping that adds a shunt pump that sends a small amout of heat backto the OWF to prevent it from freezing if it is left un-fired.

    Screenshot 2026-09-29 at 12.07.47 PM.png Screenshot 2026-09-29 at 12.10.04 PM.png
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • leonz
    leonz Posts: 1,933

    https://forum.heatinghelp.com/discussion/204922/need-help-hydronic-system-with-cast-iron-radiators

    The outdoor boiler you have is much too large for your home UNLESS you install more hot water storage and do batch burning every few days and use a heat exchanger in the home to push the homes cool water back to the heat exchanger keeping the homes circulation as a closed circuit with a second circulator.

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