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Dump zone for Tarm Wood Boiler

Leo G_101
Leo G_101 Member Posts: 87
I was just looking at a one pipe system yesterday, and was amazed to see monoflo Tee's only on the returns. I would have never guessed about the need for mono's on the supplies also if piping downward! Thanx for saving my bacon before I even got to the frying pan!

Leo G


  • Saggs
    Saggs Member Posts: 174

    I'm hooking up a Tarm wood boiler for a customer and wanted some clarification on placement of the dump zone in case of power outage or over heat situation. The manual shows the zone to be above the boiler I would say for convection purposes. Does the heat load need to physically be higher than the boiler or can the piping go up and then down to the floor where the radiation could be placed? I'm using the required N.O. zone valves and piping in a "paralell" design. Thx
  • Dave_4
    Dave_4 Member Posts: 1,405
    gravity has little influence...

    on pumped water. The only exception being the use of mono-flo fittings, where down-fed supplies and returns require dual tees; this, the result of gravity "resistence."

    I see no linkage to that dynamic, and what you ask.
  • jp_2
    jp_2 Member Posts: 1,935

    if the power goes out, what runs the pump?

    sounds like yes, the load has to be higher than the boiler.
  • jim post
    jim post Member Posts: 58
    Tarm Power Fail Dump Zone

    I piped the dump zone on my tarm using 3 parallel runs of copper fin tube mounted vertically on the wall next to the boiler. Once the power fails a normally closed valve opens and lets hot water move by gravity to the fin tubes. This pushes the cool water from the tubes back to the boiler. The dump zone loop extends probably 4 feet above the tarm and maybe 1 foot below. It works.

  • Saggs
    Saggs Member Posts: 174

    That's exactly what I needed to know, thx for the reply. How much fin tube baseboard did you use?
  • John McArthur_2
    John McArthur_2 Member Posts: 157

    I piped the dump zone in parallel to a large radiant slab for the garage. I also wired the high-limit switch in parallel with another large slab zone thermostat in case of an overload with power still on.

    Had the power fail once just after the owner stoked the thing full of wood and it sort of worked. I recommend going with larger piping that the mfg suggests to promote convection. Also make sure that you really purge the lines well or it can flash to steam. Good luck, once the bugs are out, they work really well.
  • jim post
    jim post Member Posts: 58
    dump zone sizing

    IIRC, the manual says something about sizing the power loss dump zone to handle 10% of the max btu/hr of the Tarm. Mine is a Solo Plus 30 so I used 18' of fin tube which gives me 12,960 btu/hr of dissipation. If power goes down the draft fan will too so the fire should gradually get discouraged...I have lost power several times in two seasons of operation and the heat went to the dump zone as designed.

    The tarm has worked great...once the operator errors were accounted for. :-)
  • Eric Johnson
    Eric Johnson Member Posts: 174
    water heater vessel

    What I'm planning to do is to locate a 40- or 50-gallon hot water heater above the boiler with an Automag (NO) zone valve wired to the main circuit. In theory, when the power fails the valve opens and hot water presumably convects into the tank. Lots of tappings of various sizes on an electric hot water tank, which is nice.

    My situation is complicated by the fact that the area above the boiler is unheated space, so I'll have to heat the water heater enough to keep it from freezing and hope that the tank insulation can slow down the heat loss. I'm thinking maybe a low-temp aquastat in the tank that breaks the circuit to the Automag when the temp gets below 40.

    At the moment I have a couple of cast iron radiators piped into that space, but I have other uses for them.
  • mtfallsmikey
    mtfallsmikey Member Posts: 765
    How would a person approach this

    If the Tarm was outside of the house in a separate building? Can the heat dump be at or below the same level?
  • hot_rod
    hot_rod Member Posts: 22,144
    Bit of an overkill, really

    that whole dump zone concept. The Tarms I have watched shut down rather quickly when the aquastat satisifies. Which is really the same thing that happens when the power goes out :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
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