I think that is a good question. Do we have any chemists on the forum? A couple of things that make me wonder about it. 5 or so years ago a 200+ year old white oak blew over so I was able to get many loads of firewood from that tree. After seasoning, I was disappointed in the heat that I got from some of that wood...especially some of the larger limbs. The other thing is it seems that a 6" round burns hotter than a 6" round that was seasoned split in half. It might be my imagination but it seem that way so it makes me wonder if wood can lose energy as it seasons. Other than that, I would think that as long as it is dry, it is good!
I'm not a chemist, but a chemical engineer in my former career.
Seasoning of wood involves several processes:
1) Evaporation of moisture (this is the important process for us wood burners)
2) Surface oxidation (you'll see the color change from freshly split to seasoned)
3) Evaporation of other volatile chemicals (which makes up wood's Volatile Organic Content or VOC). These VOCs are what gives freshly split wood its aromatic smell.
Dry wood burns hotter than wet wood (since the energy you'd otherwise waste on boiling off the water instead goes to heating your stove or other wood burner). You end up with a lower net energy produced per pound of wood burned (wet vs dry). Wikipedia suggests that "Moisture affects the burning process, with unburnt hydrocarbons going up the chimney. If a 50% wet log is burnt at high temperature, with good heat extraction from the exhaust gas leading to a 100 °C exhaust temperature, about 5% of the energy of the log is wasted through evaporating and heating the water vapour."
My "gut feel" is that oxidation of organics in wood related to surface oxidation produces only a dinky teensy tiny (that's a technical term, by the way) energy loss in the final fuel. If you ground a chunk of wood into fine sawdust and then allowed it to oxidize over time (constantly stirring the sawdust over time to expose new surface to the air, so that the entire surface of each little particle is oxidized), this energy loss might be more significant.
A 2005 PhD dissertation out of Sweden ( (broken link removed) ) looks at the VOCs released from evergreen wood. Depending on the type of wood & how it's processed (split, ground into sawdust,...), the VOCs seem to run 0.5 - 5 grams per kilogram. At most, this is only 0.5% of the burnable organic content of the wood, so I don't think that this process would be responsible for any significant loss of energy when the wood is burned.
Over a LOOOOOONG term, bacterial/fungal degradation of your firewood may occur. Some of the organic content of the wood is gobbled up by wee li'l bugs. This will reduce the heat generated by burning the old wood to some extent. Once again, my "gut feel" tells me that this effect would be minimal, except on small diameter pieces of wood or larger pieces that have turned punky.
From here on we will refer all chemical related questions to Dr.JJ
