Math Check BTUs Wood vs Propane

KJamesJR Posted By KJamesJR, Apr 15, 2019 at 2:03 PM

  1. KJamesJR

    KJamesJR
    Feeling the Heat 2.
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    Jan 8, 2018
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    Loc:
    New Hampshire
    I'm trying to calculate the value of wood burning in my area vs the price of LP given my appliances and need a check on my maths. This is simply a cost/performance comparison when purchasing processed wood vs buying a gas. Your mileage may vary depending on how you get your fuel and the prices in your area. Also the efficiency of your appliances.

    We'll use a common variety hardwood, one that I've burned a lot of my first season. Sugar (hard) Maple, closely comparable to Northern Red Oak, yet lower in BTU value than Hickory which seems to be a more common variety in the Mid West/South Atlantic. Hemlock is as comparable in BTUs on the West Coast areas.


    Wood Application

    Wood: Sugar (hard) maple
    BTUs per cord: 24,000,000
    Average price per cord (green) in North Eastern USA: $250 C/S/D
    Efficiency of wood burning appliance: Average 75%
    Effective BTUs per cord: 18,000,000

    Gas Application

    Appliance: Goodman, LP forced air
    BTU's per Gallon of LP: 91,502
    Average price per gallon: $2.40
    Efficiency of LP burning appliance: 96%
    Effective BTUs per gallon: 87,842

    To make to cost comparison I'm bringing LP in gallons to 104:1. This will put us at $249.6 or equal to the cost of a cord of hardwood cut, split and delivered.

    End Result:

    Effective BTUs per cord of wood: 18,000,000 (unchanged)
    Effective BTUs per 104 gallons of LP: 9,135,568
    Effective price: $250

    Wood appears to be nearly 2x's more cost effective than LP for shear BTUs given the efficiency of the appliances listed.

    Sites:

    http://worldforestindustries.com/forest-biofuel/firewood/firewood-btu-ratings/

    https://www.amerigas.com/amerigas-blog/2012/march/geeking-out-over-propane

    https://jotul.com/us/products/wood-stoves/jotul-f-500-oslo--50528

    Could not site my LP furnace as I'm unsure which model it is exactly. I do know it is a 96% efficient model.

    Please let me know if my numbers are fudged up.
     
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  2. billb3

    billb3
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    Dec 14, 2007
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    1/2 the price of propane sounds right


    There are a number of fuel comparison calculators online to verify/compare calculations


    Of course there's always how many BTU you need per hour on the coldest day of Winter and if your heating devices are capable of serving your needs. Your area is probably 45-50 BTU / sq ft
     
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  3. bfitz3

    bfitz3
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    Jan 6, 2015
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    Why not just calculate BTUs/$?

    Wood: 18,000,000/250 = 72,000BTU/$
    Propane: 87848/2.40 = 36,600BTU/$

    As you said, wood is about half the price of LP. The units of BTU/$ just feel much more intuitive.

    This makes on the fly changes possible too. If you change wood species, say to one with 20MBTU, multiply wood’s BTU/$ by 20/24. If propane dropped to $2/gal, multiply propane’s BTU/$ by 2.40/2.00 and similarly for a change in wood cost.

    I’m gonna stop before someone reports me to the geek police.
     
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  4. KJamesJR

    KJamesJR
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    Jan 8, 2018
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    Loc:
    New Hampshire
    I felt it was important to show my work. I.e. appliance efficiency. When I threw 18 million out for maple someone who knows the difference wouldn’t take up arms. My brain also likes to makes things more difficult than they need to be.
     
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