Does anyone know how wood density influences moisture content? It seems to me that the denser the wood (closer together the rings are), the lower the green moisture content of the wood would be. If so, I would expect the same species of wood could have very different potential heating BTUs per pound.
Smaller growth rings do not mean the wood is denser. There might be some relationship between density and MC, but I've never heard or read such a thing. Regardless of whether density and moisture content correlate in some way, green moisture content can vary quite a bit within species so BTUs per pound of green wood vary as well.
So if you have a tree that is 100 years old and 7 inches in diameter, it's wood is not more dense than the same species at 100 years and 14 inches in diameter? There is not more wood and less air space? Does wood with smaller growth rings inherently have lower moisture content than wood with larger growth rings? What are the factors than influence moisture content within a given species?
There are many variables that affect the distance between the growth rings. Widely spaced growth rings indicate fast growth while narrow growth rings indicate slow growth (yeah no chit). So the question is what causes the variation in growth. For a tree to grow fast, it needs a decent sized crown (30-50% of its total height), decent root structure, water, nutrients and sun. So for two trees next to each other, one with narrow rings and the other with wider rings, it is entirely possible that the one with wider rings has a better supply of water and thus has a higher, as you say, "inherent moisture content" than the slower growing tree. This doesn't necessarily make the slower growing tree "more dense". When you talk about BTUs per pound, the pound should be referring to dry (zero moisture) weight. So for two pieces of the same species with slightly varying ring structure or densities (knots are more dense than clear wood), the molecular structure of the wood is the same and thus the BTUs per pound are nearly identical. The wetter the wood is when you burn it, the more of those BTUs you lose to evaporating water. That's my take on it.
I think close growth rings do mean the wood is more dense than wood of the same species that has wider growth rings and grew faster.
I'm asking because I use a lot less wood than most other people, and heat a large home in a cold climate. My wood is from my woods, which are on limestone, with very little, albeit rich, topsoil, and are natural (have not been thinned) so are densely growing and competing for sunlight and moisture. I have a very rich flora, with grass throughout my woods (sedge, I think), carpets of wild flowers in spring and hundreds of species of mushrooms. My trees have very dense growth rings. So, I'm wondering if a cord of my wood weighs more than a cord of average wood, OR if a cord of my green wood has lower moisture content than a cord of the average wood. Right now I'm fiddling with weighing some stacked, air dried wood, computing actual volume, converting to stacked volume, extrapolating to get weight of a cord. converting to BTU's and comparing to charts. Useless (well, at least less informative than possible), though, unless I know moisture content of wood, and I have never used a moisture meter, and won't, so hate to waste the money on one, and have yet another item I never use. Last night I came up with 5400 pounds for a cord of ironwood, 5000 pounds for a cord of sugar maple, and 3900 pounds for a cord of beech. But, that was based on weighing only a few pieces of each...about 1.5 cubic feet of each, then extrapolating.
No. You can look at different types of trees to determine this. Look at the slower growing trees and you'd think they would be the same but they are not. In addition, some will give up their moisture relatively quick but then look at red oak which gives it up reluctantly. Better off to go by weight of dry wood as to which will give the best burn.
Here is a chart with a bunch of species both green and air dried weights http://www.engineeringtoolbox.com/weigt-wood-d_821.html and this one with more species but just dry weight https://chimneysweeponline.com/howood.htm If I could burn ironwood, sugar maple and beech exclusively, I'd be a happy dude and burn a lot less wood. But alas...
