Trying to keep it as simple as possible and you have to understand that the calculations are based on averages, and the results should be considered estimates. For instance, the 8600 Btu's for hardwood species is the gross value. The net value would be closer to 8050 Btu's
Under ideal conditions, one pound of oven dried wood, potentially, can produce 8600 Btu's Species with a high resin content will produce slightly higher values @ plus minus 9000 Btu's/Oven Dried Pound of wood.
Moisture content (MC) will reduce the available heat units that this one pound of wood can produce. The heat units are calculated based on dry wood and the weight of the moisture will have to be subtracted.
50% of moisture content would give you 0.34 lbs of water and 0.66 lbs of dry wood
The amount of Btu's @ 50% MC - 8600 * 0.66 = 5676 Btu's
20% of moisture content would give you 0.17 lbs of water and 0.83 lbs of dry wood
The amount of Btu's @ 20% MC - 8600 * 0.83 = 7138 Btu's
To calculate the weight of moisture % in one pound of wood:
one pound of wood = 16 oz.
10% MC adds 1.6 oz of water for a total of 17.6 oz.
1.6 / 17.6 = 0.0909 rounded = 0.09lbs of water--------- 1lbs - 0.09 = 0.91 of dry wood
The amount of Btu's @ 10% MC - 8600 * 0.91= 7826 Btu's
45% MC adds adds 7.2 oz of water for a total of 23.2oz.
7.2 / 23.2 = 0.31034 rounded = 0.31 lbs of water--------- 1lbs - 0.31 = 0.69 of dry wood
The amount of Btu's @ 45% MC - 8600 * 0.69 = 5934 Btu's
If you understand the above you can now estimate the amount of Btu's any species of wood will produce that you are burning and what the amount of Btu's are for different species based on the density (lb/ft3) of the wood you are burning.