It takes energy to dry firewood. When firewood is naturally seasoned then this energy is extracted from the outside air. When firewood is dried in a kiln then we have to use a fuel source to dry the wood. The fuel source can be oil, gas, wood waste, etc. On this page, we will review the typical energy consumption and the average cost for drying fresh split (green) firewood.
Energy cost for drying 1 cord of firewood.  

Theoretical Lab conditions 
Firewood kiln conditions 

Estimated weight of green firewood: (Oak=4900lbs, Maple, soft=3960lbs, Ash=4240lbs, Hackberry=4040lbs, Alder=3600lbs = average 4150 lbs/cord 
4150 lbs/cord  
Estimated weight of dry firewood: (Oak=3425lbs, Maple, soft=2640lbs, Ash=3180lbs, Hackberry2940lbs, Alder=2220lbs = average 2880 lbs/cord 
2880 lbs/cord 

Amount of water extracted per cord of firewood to become dried.  1270 lbs/cord  1270 lbs/cord 
How much energy will it take to evaporate 1 lbs of water: Starting temperature is 60F. Raising 1 lbs of water from 60F to 212F = 152btu (1btu = 1F per lbs) Evaporating 1 lbs of water at 212F = 971 btu. Theoretical energy needed to evaporate 1 lbs of water from 60F = 1123 btu First if there is a heat waste factor in any kiln, basically you will need significantly more heat to get this done due to heat energy escaping during venting, walls, floor, and other inefficiencies. The rule of thumb in lumber drying is 3560% waste factor. This means it will cost between 1700 to 2800 btu to evaporate 1 lbs of water in a kiln. 

How much energy does it take evaporate 1175 lbs of water from firewood: Theoretical: 1270 lbs of water x 1123 btu/lbs = 1.4 million btu (not possible) LOW Estimate: 1270 lbs of water x 1700 btu / lbs = 2.0 million btu HIGH Estimate: 1270 lbs of water x 2800 btu / lbs = 3.3 million btu 
1.4 million btu 
between: 2.2 million btu and 3.6 million btu 
How much energy does it take to raise 1 cord of firewood from 60F to about 212F: Average weight of firewood dry (with 20% water) = 2880 btu Temperature increase is (212F  60F) = 152F increase Approximately 1 btu / lbs / 1F increase. Total energy needed to raise wood temperature (2880 lbs x 152 btu/lbs) = 437760 btu. 
approx. 440,000 btu. 
approx. 600,000 btu. 
Total energy consumption to dry 1 cord of firewood: THEORETICAL: (1,400,000 + 440,000) btu = 1.8 million btu LOW estimate: (2,200,000 + 440,000) btu = 2.6 million btu HIGH estimate: (3,600,000 + 440,000) btu = 4.0 million btu Kilndirect MiniQuick Firewood kiln will be very close to the LOW estimate as that kiln design relies on "boiling" the water out of the wood and letting the "steam" escape instead of venting. 

TOTAL COST IN ENERGY TO DRY ONE CORD OF WOOD IN THE MINIQUICK FIREWOOD KILN 
1.8 million btu. 
2.8 million btu. to 4.2 million btu 
Estimated cost of energy with wood waste: 1 cord of firewood is normally between 1520 million btu (cost per cord = $0$100) 
~10% of a cord up to $13.00 
16%24% of a cord $20.00 to $50.00 
Estimated cost of energy using LPgas Each gallon of LP gas = 91000 btu / gl LPgas Current gas costs: $2.00 per gallon THEORETICAL: 1800000 / 91000 btu/gl = about 20 gallons LOW estimate: 2800000 / 91000 btu/gl = about 31 gallons HIGH estimate: 4200000 / 91000 btu/gl = about 46 gallons 
$40.00  $62.00  $92.00 
Estimated cost of energy using Natural gas 1 cubic foot of Natural gas = 1000 btu (100 cu.ft = 10 Therm) Current average cost for 1 Therm of natural gas: $1.50 per Therm THEORETICAL: 1800000 / 100000 btu/Therm = about 18 Therm LOW estimate: 2600000 / 100000 btu/Therm = about 26 Therm HIGH estimate: 4000000 / 100000 btu/Therm = about 40 Therm 
$27.00  $40.00  $60.00 