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Wood vs. Oil #'s

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by chuck172, Jun 23, 2008.

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  1. chuck172

    chuck172 Minister of Fire

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    My Tarm is being delivered today. Solo40. I'm looking at my wood shed and I have that warm feeling. I have 7 cords stacked seasoned, ready to go, another 5 cords split and heaped up for next year. More on the way.
    I'm wondering. 12 cords= 1800gal. of oil
    @4.50/gal.=$8,100.00
    Wow, when I get done burning all that wood I will have paid off the boiler+
    That's calculating 1 cord =150 gallons. What I'd like to know is what efficiencies are we talking about. The gasifiers are more efficient than regular wood stoves. Does the cord to gallon formula still hold true?

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  2. webbie

    webbie Seasoned Moderator Staff Member

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    Here is the problem with such calculations - each type of wood has a different heat value per cord. Even within a species, the density can vary!

    Since wood is sold by cubic size...as opposed to weight, one cord can weigh twice as much as another.

    But your area is blessed with a lot of hard woods. Still, it can make a difference of as much as 50% more heat value in a cord of one wood as compared to another.....

    Take some time to study the articles on wood heat values - as well as the Fuel Cost Comparison:
    http://www.hearth.com/compare

    Here are some rough figures - a medium density cord of wood - dry - would weigh 3200 lbs or so. That wood contains approx 7000 BTU per pound when it is adjusted for moisture.

    Multiply those out.........about 230,000,000 BTU's

    OK, so how many gallons of oil is 230K BTU? Divide it by 140,000 or so (BTU in a gallon of oil) and you will come up with about 160 gallons of oil. In the case of a TARM, we can probably assume the same efficiency as most oil burning boilers, so that part is a wash.

    If you get lucky and get a better (harder, denser) species of wood, a dry cord can weigh as much as 4,000 lbs. Based on eastern hardwoods it might be safe to say that a cord = 160 to 200 gallons of oil. BUT, if one was to burn the same wood in a much less efficient system, all bets would be off. It would be easy to 1/2 those numbers or worse, based on the efficiency of the appliance. Therefore a boiler with older technology may replace 100 gallons of oil with a cord.....some even less.
  3. chuck172

    chuck172 Minister of Fire

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    Maple, oak, hickory, birch. So 160-200 gallons. That's great. Knowing this gives me inspiration to keep cutting. thanks.
    P.S Delivery was just delayed till tomorrow morning.
  4. free75degrees

    free75degrees New Member

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    Do you think that the interior of larger diameter logs is denser than narrower logs? It seems like the 30" plus diameter oak is very dense compared to narrower oak, but maybe it just seems like that because it is so heavy.
  5. chuck172

    chuck172 Minister of Fire

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    I think he meant Hard maple vs. Soft or Red Maple for example.
  6. webbie

    webbie Seasoned Moderator Staff Member

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    No, I meant heartwood of the same species.........i think it probably depends on climate, soil, the sun (spacing) of the trees as well as other factors, but the experts usually give a range of densities for even the same species. Heck, we've all bought framing and other lumber and seen where one piece of the same species and moisture can weigh more than another (closer grain).

    That is why wood will forever be a mystery......you can't nail it down! (so to speak). Each piece differs, just like a fine Jersey tomato or strawberry.
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