I have been keeping the fence-post size pieces and cutting up the other into stove-wood for Sprite.
I was curious about how much moisture was in the wood. Consequently, I asked Sprite if she would mind if I kept a couple of 7" diameter chunks. She was fine with that. The outside temperature when we cut the wood today was 20F so most of the sap had been driven back down to the roots.
I split the rounds into quarters, then I cut one of the more typical looking quarters into a 5.25" long sample. The triangle measured out as 0.0185 cubic feet and weighed 636 grams (1.40 pounds) or 75 pounds per cubic foot.
The reason I cut the sample to 5.25 inches of length was so I could fit it into the microwave for drying. The protocol is to put it into the microwave for a minute or two, then weigh it. As long as it continues to lose weight it is still giving up moisture. If the weight loss diminishes or you smell scorched wood...you are done.
The final weight was 415 grams (0.91 pounds) or 49 pounds/cubic foot. It indicated a sample moisture content of approximately 35%.
The problem with moisture
If the 0.91 pounds of dried wood were perfectly combusted it would release about 7500 BTU.
Heating up the 0.50 pounds of moisture from 60F to 212F would take 75 BTU and boiling off the 0.50 pounds of water (liquid-to-vapor) would consume another 480 BTU for a net gain of about 7000 BTU for the original 1.4 pound chunk.
It gets worse if the chunk is frozen and immediately pitched into the woodstove.
Let's say the wood is 20 degrees F. It would take 96 BTU to raise the water content from 20-to-212 degrees, another 70 to thaw the half pound of water and an additional 480 to boil off the water. That leaves a net gain of about 6850 BTU for the chunk of wood that originally weighed 1.4 pounds.
If the wood was 50% moisture by weight then a 1.4 pound chunk has a gross BTU potential of 5740 BTUs and it would take 134 BTU to raise the temp from 20F, 100 BTU to melt the ice and another 660 BTU to boil off the moisture. The 1.4 pound chunk would net 4800 BTU or only 70% as much as the 35% moisture wood.
|Even at 35% moisture it burns well when placed on a bed of coals. It burns with very little flame. Without the bed of coals it seems as flammable as concrete. Six hours ago the wood in this fire was still in a live tree.|