# Math Check BTUs Wood vs Propane



## KJamesJR (Apr 15, 2019)

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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## billb3 (Apr 15, 2019)

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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## bfitz3 (Apr 15, 2019)

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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## KJamesJR (Apr 16, 2019)

bfitz3 said:


> Why not just calculate BTUs/$?
> 
> Wood: 18,000,000/250 = 72,000BTU/$
> Propane: 87848/2.40 = 36,600BTU/$
> ...



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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## Soundchasm (Apr 25, 2019)

A benchmark I've used that I believe to be reliable is that one cord of wood equals 100 gallons of fuel oil.  Is it true?  I have no idea.  Seems pretty magical.  But if so, how convenient.

I calculate how many cords I've burned and multiply it by the price of fuel oil.  I then look at the time I spent C/S/S to figure out how much I was paid to process my firewood.

You could look at the relationship between fuel oil and LP BTUs and use it as another angle to verify your findings.


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## billb3 (Apr 25, 2019)

Soundchasm said:


> A benchmark I've used that I believe to be reliable is that one cord of wood equals 100 gallons of fuel oil.  Is it true?  I have no idea.  Seems pretty magical.  But if so, how convenient.
> 
> I calculate how many cords I've burned and multiply it by the price of fuel oil.  I then look at the time I spent C/S/S to figure out how much I was paid to process my firewood.
> 
> You could look at the relationship between fuel oil and LP BTUs and use it as another angle to verify your findings.




One equivalency metric for home heating oil  is 138,500 BTU per gallon. Ratings for wood species vary but 14 million BTU for a cord of eastern white pine would be roughly equivalent to  100 gallons of fuel oil. Oak at 24 million BTU per cord would be equivalent to 170 gallons of heating oil. 

If you really want to "pay yourself" take that money you didn't spend on fuel oil and it invest it and grow it somewhere somehow.


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## SpaceBus (Apr 25, 2019)

billb3 said:


> One equivalency metric for home heating oil  is 138,500 BTU per gallon. Ratings for wood species vary but 14 million BTU for a cord of eastern white pine would be roughly equivalent to  100 gallons of fuel oil. Oak at 24 million BTU per cord would be equivalent to 170 gallons of heating oil.
> 
> If you really want to "pay yourself" take that money you didn't spend on fuel oil and it invest it and grow it somewhere somehow.



This is what I'm going to do once we finish fixing the house! It's amazing what even a tiny amount of money invested into an annuity every month can do.


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## Soundchasm (Apr 26, 2019)

billb3 said:


> One equivalency metric for home heating oil  is 138,500 BTU per gallon. Ratings for wood species vary but 14 million BTU for a cord of eastern white pine would be roughly equivalent to  100 gallons of fuel oil. Oak at 24 million BTU per cord would be equivalent to 170 gallons of heating oil.
> 
> If you really want to "pay yourself" take that money you didn't spend on fuel oil and it invest it and grow it somewhere somehow.



Excellent advice.  Luckily, my younger self took care of that.  ;-)  I choose to turn profit into guitars these days!


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## KJamesJR (Apr 27, 2019)

Purchasing and installing my wood burner WAS an investment lol

A penny saved is a penny earned.


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## Soundchasm (Apr 27, 2019)

I've explained to my wife many times that savers are lousy spouses but great ancestors!!


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## KJamesJR (Apr 28, 2019)

Soundchasm said:


> I've explained to my wife many times that savers are lousy spouses but great ancestors!!


Well it just harkens back to putting those extra pennies elsewhere.

I “made” $300 this year (my first year) with the stove. Probably would have still been in a slight deficit had I contracted out all the install work. It’s all money in the bank after this.


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