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.|
|Estimated weight of green firewood:
(Oak=4900lbs, Maple, soft=3960lbs, Ash=4240lbs,
Hackberry=4040lbs, Alder=3600lbs = average 4150 lbs/cord
|Estimated weight of dry firewood:
(Oak=3425lbs, Maple, soft=2640lbs, Ash=3180lbs,
Hackberry-2940lbs, Alder=2220lbs = average 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 35-60% 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
2.2 million btu
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.
|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
Kiln-direct 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.
4.2 million btu
|Estimated cost of energy with wood waste:
1 cord of firewood is normally between 15-20 million btu (cost per cord = $0-$100)
|~10% of a cord
up to $13
|16%-24% of a cord
$16 to $24
|Estimated cost of energy using LPgas
Each gallon of LP gas = 91000 btu / gl LPgas
Current gas costs: $2 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||$62 - $92|
|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: $1.25 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
|$22.50||$35.00 - $52.50|