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Primary piping outdoor non-pressurized boiler


2 years ago, I bought the "pumping away"  and "Prim./Second" books.  Read them and installed a textbook system for an indoor pressurized corn fueld boiler.  Never used it much due to flue/smoke issues.   Switched to an outdoor non-pressurized system.   I moved my circulator (taco 007 F5) to the outdoor boiler shed so this puts it "before" the expansion tank/seperator.  Will that make a difference in this non-pressurized system?  I'm dealing with Gremlins.  My secondary loop is a Flat Plate heat exchanger.  The load side of that exchanger is between my supply/return on a propane boiler.  I have the propane boiler isolated.  I am not circulating hot water through the propane boiler.

When I created my primary loop, I installed a gate valve between the Tees.  If I turn-off the load zones (secondary loop) and let the primary recirc on itself. the boiler will reach setpoint at a rate of 1°/minute.  The boiler holds about 35gal.  If I have the valve between the Tees "open" or "closed" my water temp. slowly decreases.  I have 800' of 5/8 tube in "warmboard".  (6 loops, 2 zones). Mixing valve delivering 110° water to the floor.  The other zone is baseboard for 1200ft² of house in wisconsin.  I was heating all of this with a Burnham Series 2 (About 66K BTU/HR out, until it developed a leak between the exchanger plates.

I have many more pertinent details.

Do I have a flow "gremlin" due to the "Wrong" location of the circulator in the Primary/secondary un pressurized system?

Thanks in advance,



  • kcopp
    kcopp Member Posts: 4,432
    a diagram is.....

    really needed here. Seems the wood boiler should be going through the flat plate/ HX and if its a non press / open set up you need a high head bronze/ SS circ....
  • Timo2le
    Timo2le Member Posts: 3
    High head circulator

    Thanks for taking the time to reply.  I will work on a diagram.   I did alot of work on the burnpot/fire/fuel side to make sure I have the best heat source possible.  I restarted the boiler with FP HX loop closed (secondary), and had my gate valve in the primary loop open, and let the boiler recirc on itself, until setpoint was reached.  Then I enabled the secondary loop (opened valves and powered the circulator).  I'm heating the house this way, so the secondary must be getting it's water fromt he primary.  Again, I do have the gate valve between the Tee's OPEN, so the pri/sec is working as planned.  I don't know what the pressure differential is, so I don't know if I'm just getting lucky.

    I will create a diagram and add some pictures.

  • RobbieDo
    RobbieDo Member Posts: 131
    Bronze pump

    A bronze or SS pump is a must with a open system. I have installed many outside wood boilers, I always heat the inside backup boiler with the outside boiler, this makes the inside one work less when it calls for heat, but it must be setup properly. A flat plate heat exchanger must be used also. Do you have a dump zone in case the outside unit over heats? Pics or diagram would be helpful also. Thanks
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