That's one of the good things learned here, BTU content of various woods differ greatly.
Makes members & readers of the forum, more educated & better wood burners
Charts vary with moisture content (20% is the norm) & how many BTU per pound (
8000 to 8500) & volume in a given cord (80 - 90 cubic ft of wood)
* 8,000 to 8,500 Btu per pound for non resinous woods. 8,600 to 9,700 Btu per pound for resinous woods @ 12% moisture.
8,000 to 8,500 BTU per pound is quit a span, most charts use these numbers to calculate BTU per cord, so you get quit a range of BTU like:
Douglas-Fir @23.5 - 26.5 Mil BTU/cord.
Important also, are charts that give weight per cord, dry & wet (green). Helps you not overload your rig too much
Bottom of this chart give some of the critera used to calculate the numbers: (
Notice 12% moisture content used)
http://www.consumerenergycenter.org/home/heating_cooling/firewood.html
Mother nature is not perfect. Random is more realistic.
You don't see trees of the same species exactly the same, some have better soil, sun, water & climate than others & grow faster. Some grow slow & have tighter grain.
Seeing variances on BTU is "natural", even trees a few yards apart will vary.
I've thought of doing some testing with the birch here, called "paper birch" but has the BTU of "yellow birch" (test done by UAF) years ago.
But, would it mater? Birch would still bet the best BTU wood here.
Someday, wood might be sold by BTU instead of cord. Then more samples & testing would be important.
Here we ask, how many cords do you burn per year, maybe how many Million BTUs will eventually come along, (we have a member good at it, but has not been here for a while)
I know if prices per cord were all the same, I'd want a cord of birch over a cord of cottonwood
The charts get you close & let you know which species you get "the most bang from your buck"
Dry wood is the most important part of burning wood, 20% is minimum, less is "soooo" " sooo" much better. (Boiling water takes energy from the heat return & creates creosote)
The new catalytic stoves, really really like dry wood
I've learned "You burn what you got" , & the drier, the better