Tarm MB 40 What To Watch For

roughidle Posted By roughidle, Oct 25, 2018 at 10:01 AM

  1. roughidle

    roughidle
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    Nov 2, 2017
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    I'm going to look at a used HS Tarm MB40 ?Mark 2? tomorrow after work. Selling for $200. I am looking to upgrade to a boiler as we are in the middle of a complete home renovation and will be installing a central air system. I wanted a boiler so I can run the hot water to a coil in the air box. Right now, we are just running a conventional wood stove.

    What should I be looking for in this unit to give red flags? Specific failures (if any)?

    We have a local boiler repair and maintenance company that I've contacted that are willing to pressure check it for me, but I was hoping to get some additional information from seasoned users that may be able to shed some light on unseen issues.

    Thanks
     
  2. hobbyheater

    hobbyheater
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    This boiler is old technology .Look for gasification with storage , but you will be laying out $ 20,000 not $ 200 !
     
  3. roughidle

    roughidle
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    Which is why right now I'm not buying a gasification boiler. However, installing a boiler such as this old technology will allow me to plumb and use my heating system in the same way as I will as when the "some day" comes that I'll be able to afford and install a gasifier.

    But thanks for your input.
     
  4. maple1

    maple1
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    Any signs of corrosion. Any signs of abuse or improper operation.

    That should all show up in heavy creosoting in the firebox area. The most likely spot for corrosion is bottom of firebox. Closest to the return fitting.

    That is just general talk applicable to any boiler.

    Do you have plans to add storage in the future? With a central air system, and if there is no storage in the future, or nothing else you will be heating, I would be inclined to just go with an add-on wood furnace vs. a boiler. That would avoid having to deal with things like expansion tanks and overheat/dump protection - using the boiler just to heat a W-A coil doesn't leave anywhere else for heat to go if you need to put it somewhere. It might also spend quite a bit of time idling. You might be able to add some rads on somewhere, though - should at least add something else on for dumping.
     
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  5. Bad LP

    Bad LP
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    I gotta agree with Maple1 on this. Installing a boiler to heat water only to dump it into a water/air exchanger is an extra step and parts. I'd be looking for a wood furnace.
    If you have plans for hot water heating in the future then that's a whole other topic but it sounds like that is not your plan. I also have reservations about an old school boiler choked down fouling up the chimney.
     
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  6. roughidle

    roughidle
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    I did plan on using this to offset costs for home heating potable water. It comes with a heat exchanger for that.

    I wanted to try and add another hot water tank to store some water, but wasn't sure if another 80-100 gallons would be worth it. At the current moment until more of the renovation is complete, I do not have the room for a much larger water tank.
     
  7. Bad LP

    Bad LP
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    I'm not overly thrilled with making DHW off my wood boiler. I'm planning on putting DHW back onto the System 2000.
     
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  8. maple1

    maple1
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    Yes, that much storage won't accomplish much. I would consider 500 a bare minimum. I have 660 and would really like to have 1000.

    Everyones DHW situation is different - but in my case I would just do that with an electric tank heater and go with the furnace. That only costs us about $25/mo here with 0.18/kwh electricity, for summer months. DHW heating is a pretty small part of a heat load. I have been figuring it is about 1/30 of our space heating load. Real rough round numbers. If you have NG or LP on site already that would be another story. What will be your other heat source? A heat pump water heater is another possibility.

    Also, some furnaces have add-in DHW coils as an option. Not sure how many & which ones - but there are some.
     
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  9. sloeffle

    sloeffle
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    In the winter time my wood furnace indirectly heats my hot water. We have a HPHW not too far from the wood furnace. The excess heat coming from the wood furnace is turned into hot water via the HPHW. In the summer time I no longer have to run a dehumidifier in the basement too since the HPHW dehumidifies my basement.
     
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  10. 3fordasho

    3fordasho
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    I do the same - my HPWH is a few feet away from the wood furnace. I was never a believer in electric water heating until the heat pump version came around, now I'll never go back to gas or straight electric water heating. I've never had to use the back up elements either, all water heating for the two of us and occasional guests has been accomplished with heat pump mode only. Now if I had a couple teenagers around it would be a different story..
     
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  11. JMihevic

    JMihevic
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    Feb 3, 2018
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    If the Tarm MB 40 boiler is in good shape I would go for it. I have a Tarm MB 55 that I installed in 1980 when I built my home. The contractor installed a heat pump. I sized a two row hot water coil that I had him mount in the air plenum above the air handler. I have used it every year and it is still operating without any problems.

    My basic flow control to the water coil consists of two valves in parallel, a ten turn Hoke trim valve and a hydronic zone valve. The zone valve has a balancing cock in series for flow adjust. The zone valve is controlled by a thermostat in the main living area. This valve modulates the flow by increasing or decreasing the total flow through the water coil. I always have a minimum flow through the Hoke trim valve. I open the Hoke valve based on the outdoor temp--3 turns at 30 Degrees, 5 turns at 25 Deg, and wide open at 20 Deg. At outdoor temperatures below 20 Deg, the zone valve/thermostat modulates to maintain the house temperature. Water flow is never shut off to the boiler so there is always a heat load. With this set up, my heat loss to the outside is equal to the heat output from the boiler. I run the boiler temp at 175 Degrees. The Samson draft regulator does a fantastic job of controlling the boiler water temp. When using the wood boiler, to heat our house, the temperature is more constant than when I use the heat pump.

    For domestic hot water, when heating with wood, I have a 40 gallon Amtrol Boiler Mate. The Boiler Mate has a thermocouple that controls a zone valve for control of the DHW temperature.

    I know the trend today is to go with an efficient gasifier type boiler to reduce wood consumption. My MB55 is less efficient, but I have an abundance of wood--mostly ash. Each spring, I have a fresh fall of trees (courtesy of the Emerald Ash Borer). I am happy with the simplicity of the MB55 controls; a mechanical draft regulator and no electronics to fail. I have not replaced one single part in the boiler in the 38 years I have had it heating my home! Also, I am surprised that I only have to clean my chimney and MB55 once a season. Creosote forms in the boiler but when it gets thick enough and the fire gets hot enough it burns and flakes off in the boiler. I get very little creosote in the chimney (loose & flakey) which I clean once a year.

    John M.
     
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