KarlP said:
I estimate an average of 21million per cord * 65% going into the house * 4 cords per season * 5.5 seasons = 300 million BTU. Somewhere around 3700ccf of ga$ not run through my 79% efficient furnace...
So far its needed one door gasket replaced and I've cracked two firebricks. I recently cleaned it and see no other wear. I see no reason why I won't get over a billion BTU out of it during its lifetime...
What kind of wood did you use most of the time? Most published BTU figures were established in a lab with oven-dried wood in a bomb calorimeter and including 100% capture of the latent heat of condensation. The real world low heat values of those woods are about 10-15% lower than published tables quote (depending on the moisture content of the wood when burned). Doesn't really matter for burning purposes, but you have to include that loss when making comparisons with other heat sources.
Anyway, I'll play.
Using a mix of ash and cherry which is mostly what I've burned for the last 18 years in my previous stove, I'll accept your average as pretty close. 21 million x 55% (inefficient stove) x 4.5 cords per season x 18 seasons = 935,550,000 BTH. I retired the stove this year, otherwise I'd have been able to join the "Billion BTU" club with it.
I traded a few hours work for that stove and rebuilt it myself. I paid for only a tube of stove cement and some gasket material, a few 6" elbows, a flue pipe damper, and about 6' of 6" single wall stove pipe running it directly into a tiled masonry chimney in the basement. Oh... about every three years I had to buy about $30 worth of 1/4" steel plate to improvise replacement side baffles that I burned through by running the stove so hot.
I have electric baseboard heat, so the equivalent energy consumption would be 275,000 KWH. At an average of about .10/KWH (I pay almost .15 right now) for the last 18 years, that is $27,000 I saved. Of course, I spent about $6000 on wood, so that's $21,000. Not as much as I thought, but still real sweet for a free stove. But... if I had used electricity all those years, my wife would have been bumping up the thermostat all the time, probably increasing the actual usage by 20-25% - about what the wood cost me - so now I'll call it $27,000 again. By burning wood instead of using electric, all I had to do was buy her lots of sweaters and comforters, remember her birthday and Valentine's Day and tell her she looked real pretty shivering like that.