Here let me rephrase "A square foot (or a cord) of wood dried from 100% MC down to 0% MC would yield a lot more btus, even with the small amount of volume reduction (shrinkage) that occurs."
Moisture, is the same either way, in that it doesn't burn. Now, wood that was dry, and then wetted from rain however usually only sits on the outermost parts of the wood, while in unseasoned wood, the moisture is all the way through the piece of wood.
I view wood as btu's based on weight, more so than by volume. I will gladly take 1 cord of shagbark hickory vs 2 cords of basswood to keep the house warm for a winter. The heavier the wood, provided it's dried, the more btu's there is.
And yea, 100% moisture would be just that, a bag of water with no wood...... A good rule of thumb that i heard a while ago is that for every 1% moisture content to your wood, you lose 1% in efficiency. The chart basically backs that up except at the extreme high and low ends. Soooo, if you have a stove that is 85% efficient when tested with 15% wood, and you burn 20% in it. Then the actual efficiency that you are getting is 80%. The way i like to look at it is that for every 1% of moisture my wood loses, my stove gets 1% more efficient, and i save 1% of the effort in C/S/S required to heat my house.
I have a hard time believing the BTU's are the same from wet wood to dry wood. Take your 1 pound of wet wood dry it down to a 1/2 pound lite it on fire and then take that 1/2 pound of water that came out of it and pour it on the fire and then tell me how many BTU's you are getting.
The btus remain the same, but they are "lost" to you if they are used to convert water to steam, which then goes up the pipe, rather than heating the stove.
You know in this discussion all I hear is the btu's in wood does not change from dry wood to wet wood. What I do not hear is the effect that the water has on those btu's. You can have a piece of wood that puts out 3000 btu's but if you have another element in the mix such as water, that is capable of countering a part of those btu's then wet wood and dry wood are not the same. Like bushpilot mentioned. You get steam not good dry heat.
I have been hearing that, are you reading all the posts? Even Dave's chart at the beginning of the thread makes that pretty clear that extra MC in the would is not good thing. However some people use steam to heat their homes.
To use steam to heat your home the steam needs to stay inside the house. In most cases it is contained within a separate system from the combustion system, in fact I can't think of a functional system where that is not true. Dumping that steam out the stack with combustion products is a total waste of that part of the heat content of the wood. Going back a few posts, who the heck measures wood by the square foot? Sometimes we measure by volume like for example a cord but square feet makes zero sense. Measuring by weight or volume needs to always be adjusted to reflect what is being weighed. Are you measuring wood plus water content or just wood. If just wood, how much added water volume/weight do you need to deal with? Without those answers the measurement is almost meaningless.
I have read all the posts. So you tell me then what effect does the water have on the btu's and burning wood. With your comparison of a 1/2 pound of dry wood verses a pound of 1/2 wood and 1/2 pound of water and they put out the same btu's. Not in the real world.
If you read my first post you'll notice I begin by saying "According to the chart" as a disclaimer. I was just playing with the numbers. I agree that burning wet wood is an inefficient way to heat your home, and probably impossible with very wet wood. Also, as someone already pointed out, 100% MC in wood is probably not even possible either.
Now that we have that all figured out Multiply that by your stove's efficiency rating , how much of those BTUs gets into your house ? I can brag about my 82% efficient stove .....BUT ??? http://www2.epa.gov/sites/production/files/2013-08/documents/certifiedwood.pdf : My BK cat 1107 stove claims 82% My guess is the test is Under perfect conditions, probably my basement installed stove, with a year old cat, don't get 82% Maybe 70% ?
I was going to dig that up, you beat me to it. The thing to understand about MC content in wood is that it takes a certain amount of btus to cook the water out of the wood before the wood can actually burn.... The steam, unless its under pressure, can only exist at 212 degrees fehrenheit, well below the burning temp of wood. This is why your logs wont light until all the hissing and boiling gets done, Btus are being consumed to do the cooking and not the heating of your home. There are no arguements that the piece of wood has the same btus wet or dry, just how they are being used in a wet or dry situation, and how many of those btus go into your house or up the pipe as steam....
This is from the manual that came with my boiler. Shows how many kilowatts is produced per Kg at a particular moisture content. Big difference between 20% and 40%.
6845 BTUs/1 lb of wood I put in about 80 lbs for a full load. 547,600 BTUs per load x 82% = 449032 btu into the house over a 24 hour period, with 25° OAT Not bad for using a renewable resource Pretty good stove too.
