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Anyone Hear of Thermo-Control Boilers?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by otsegony, Nov 12, 2007.

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  1. otsegony

    otsegony Member

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    I ran across this wood burning boiler on the net and realized the company is just down the road from me. Has anyone heard of them? The design and cost seem really tempting since I am looking for a system that will tie in with an existing OHW radiant system for space and hot-water needs. Any feedback would be appreciated.

    http://www.nationalstoveworks.com/

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  2. webbie

    webbie Seasoned Moderator Staff Member

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    They were relatively popular back in 1979 and 1980. After that, I didn't hear about them for about 20 years, and then I saw them again online!

    In general I think if one can afford the new clean burning designs, that is the way to go.

    I'll let Eric and other chime in on this.
  3. Eric Johnson

    Eric Johnson Mod Emeritus

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    It looks to me like a conventional (read inefficient and smoky) boiler, with a (probably futile) effort to attain secondary combustion in that back chamber. In my experience with boilers of this basic type (I've owned two and installed 3), they produce a lot of good heat, burn a lot of good wood and smoke excessively at inconvenient times and can produce a lot of creosote--especially if you're trying to burn unsplit wood like they suggest.

    My standard advice to somebody considering an outside wood boiler (OWB) is that if wood supply and smoke are not an issue, then you'll be happy with a boiler like that. Same goes for one of these, except that creosote becomes an issue, since it's designed to go into your basement. Boilers like this are also a lot cheaper than the alternatives--probably half of what you'd pay for a gasifier or an OWB.

    My uneducated take on this design is that it has clear limitations, mentioned above, that anyone who owns or operates one can attest to. Don't believe wild claims by the manufacturer or dealer about efficiency or clean burning or secondary combustion. Claims like this imply a way around the laws of physics and boiler design that simply doesn't exist in the real world.
  4. otsegony

    otsegony Member

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    Eric:
    Not to belabor the point, but there are a number of boilers that seem to be in this class of appliance that look fairly similar to me and run at about half (or less) of the cost of the Tarm and other gasification units. Cost is an issue with me and I need to purchase a product that can have a reasonable pay-back period. I can see some obvious differences with the gasification technology, but could use some guidence as to how they are different in other respects. Two others that area dealers have tried to sell me are:

    Harman wood boiler:
    http://www.harmanstoves.com/features.asp?id=31

    New Yorker wood boiler:
    //www.newyorkerboiler.com/lit/Fuelsaver.pdf

    Is your opinion of these two indoor wood boilers the same as the Thermo-Control? They seem to be a tad more up market with better sheet metal and perhaps design but otherwise fundamentally similar. I would appriciate your thoughts.

    Garet
  5. Eric Johnson

    Eric Johnson Mod Emeritus

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    It's confusing, no doubt about that. And cost is always an issue with me, too.

    All I have to go on is experience, so I may be wrong. But this is the way I understand the situation:

    A gasifier is a fundamentally different design than what I'm calling a conventional wood-fired boiler. In the latter, you have a firebox surrounded by a water jacket, usually sitting on top of a grate and an ash chamber. Air comes up through the grate and burns the wood, with the smoke exiting out the back and up the chimney. You can put in various baffles and water channels to increase the heat transfer efficiency, but you can't get the temperature in the firebox high enough to achieve secondary combustion. So the result is smoke and creosote under most conditions. You can get conventional boilers with blowers or with thermo-mechanical controls, preheated combustion air strategies, etc. but they all operate basically the same way. And OWBs are simply bigger versions of indoor boilers. They're just parked out back, which has some distinct advantages and disadvantages that don't affect their efficiency.

    Gasifiers are based on a different design. A gasifier has a very similar firebox, but it's sitting on a refractory-lined combustion chamber which the smoke produced in the firebox is drawn down into and ignited at about 2,000 degrees. So instead of going up into the chimney, all smoke and wood gas is sucked down into the lower combustion chamber and burned up. What's left is hot gas, which then travels through a firetube heat exchanger immersed in water on its way to the chimney outlet. Compared to a conventional boiler, gasifier stack temps are very low (300-400 vs 500-1000), indicating efficiency, since the heat is going into the water and not up the stack. And what does go into the stack is clean--no smoke and no creosote, so no need to maintain a high stack temp.

    The bottom line, as I mentioned earlier, is that you can't achieve secondary combustion in a water-jacketed combustion chamber. Conventional boilers write off the loss and send it up the chimney. Gasifiers get the job done somewhere else and reap the benefits. As a result, conventional wood-fired boilers are typically 30-50 percent efficient, whereas a gasifier is going to be 80 to 90 percent efficient. That's overall efficiency--combustion efficiency plus heat transfer efficiency. Conventional boiler claims of high efficiencies are only giving you one or the other, depending on their particular strengths, not the necessary combination of both.

    So yes, you'll pay a lot more for a gasifier. But if it gets the job done with half the wood and with no smoke, then it's going to make up the difference eventually. You might save money over the short term, in other words, but it won't come without a cost. Having to buy or cut twice as much wood is just one example. Fouling the neighborhood air is another.

    As to recommending one conventional boiler brand over another, I think it gets down to the bells and whistles and manufacturing quality. Thicker boiler plate is always better. I think round is better than square. I've owned a Marathon and a Royall and enjoyed using both of them. If you want a conventional boiler that's going to last forever, consider either a Royall or one of those imported cast-iron rigs that New Horizon sells for about $4,000.
  6. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    Oh C'mon Garet! With that extra money Otsego County sent you for over-paid taxes, surely you can upgrade to newer technology!

    But seriously, the point made earlier about overall efficiency is so important. figure out what's most important to you and go from there:

    Low-maintenance long-lived unit
    Lowest possible fuel consumption
    Lowest possible emissions
    Longest possible burn-cycles
  7. Eric Johnson

    Eric Johnson Mod Emeritus

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    Otsego
    Owego
    Otego
    Oswego....


    Where does it end?
  8. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    Thats what my wife wants to know. In September, she said she was worried because I had NO wood for thisyear. I said I was getting 20 loads to make the winter . . . we're on 24 now and she wants to know . . .

    where does it all end??


    Can you EVER have TOO MUCH wood?? :lol:
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