Q&A boiler install

QandA Posted By QandA, May 23, 2002 at 2:20 PM

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  1. QandA

    New Member 2.
    Staff Member

    Nov 27, 2012

    Howdy- I am interested in installing a wood/coal boiler on to my existing down draft propane furnace. I am looking at a Tarm MB Solo Boiler Model #40. I called Tarm and wasn't satisfied with the info they gave me. My questions are 1) How do I size my heat exchanger that sits in the plenum(ductwork) to this boiler 2) What size circulating pump do I need 3) How do I hook up my present furnace thermostat so I can run my fan which will blow air over the heat exchanger or do I have to hook up another one and if so how is it done. 4)Am I missing anything on hooking up this Tarm boiler. Thanks for your time and help. Great website-lots of information.


    The coil is sized by the company that provides it. Typically, you'd use one which could handle up to approx 120,000 BTU for that boiler even though the normal output is likely to be 30-50K.

    Even the smallest Taco or Grunfoss hydronic pumps can easily handle this load.

    The controls might work like this...

    1. New Thermostat activates pump (note: pump is controlled so it will not run unless water is above 150 degrees.)

    2. Additional aquastat control located on output of coil in turns on furnace fan when water temps are above a certain level.

    It should be as simple as that, although you may have to fiddle with exact settings so it works best in conjunction with your existing furnace. Normally, this is best done by keeping the house thermostat 5 degrees below the new boiler one so it doesn't call for heat unless the boiler cannot produce enough
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