Nothing can make firewood sales go up quite like temperatures
going
down. But University of Georgia
scientists
say buying firewood to burn right away can lead to problems if
you don’t
get seasoned wood.
It isn’t always easy to tell if firewood is dry enough to
burn well,
said Julian
Beckwith,
an Extension
Service wood products
specialist with the D.B.
Warnell School
of Forest Resources at UGA.
The best indicator, he said, is weight.
“When firewood is cut, it holds a lot of water — up to 50
percent of
its weight,” he said. “In fact, one fresh-cut cord of oak
firewood can
contain nearly enough water to fill six 55-gallon drums.”
In a wood-burning stove or fireplace, that wood has to dry
out before
it will burn, he said. And boiling off the water steals a lot of
heat away
from the house.
“The critical word when buying firewood is ‘seasoned,’”
Beckwith said.
“Seasoned means the wood has been dried to a level that will
allow it to
burn easily, and to give up a high proportion of its heat value.”
Because of the water in it, unseasoned wood is heavier than
dry wood.
If you don’t know whether your firewood is seasoned, Beckwith
suggests
comparing its weight to seasoned wood of the same type. Use a
bathroom
scale to weigh a fixed volume, such as a cardboard boxful, of
each.
There are other signs of wet, fresh-cut wood.
“Split a fireplace log and look at the split surfaces,”
Beckwith said.
“Recently cut wood will have a darker, wet-looking center with
lighter,
drier-looking wood near the edges or ends that have been exposed
since
cutting.”
Wet wood will be easier to split than dry wood, too. And when
firewood
is very fresh, he said, the bark will be tightly attached. Bark
on very
dry logs usually can be pulled off easily.
Pound for pound, all seasoned firewood produces about the
same heat,
Beckwith said, although pine may yield slightly more heat per
pound because
of natural resins in the wood.
But woods vary greatly in density. Oak and hickory logs weigh
more than
sweet gum or pine logs of the same size. So it takes more pine
or sweet
gum logs to produce the same heat as oak or hickory.
Beckwith said the gum-like resins in pine wood lead people to
think
pine produces more residue or buildup, called creosote, than
hardwood.
But it doesn’t. Burning any seasoned wood in full, hot fires
will avoid
creosote buildup.
“Creosote buildup on fireplace or wood-heater walls, chimneys
and flue
pipes,” he said, “seems more a result of burning wood at
relatively low
temperatures.”
When wood is heated, he said, some of its chemical
ingredients are first
changed to gases and then ignited if the fire is hot enough. At
temperatures
too low for them to burn, though, they become part of the smoke.
“If these gases contact a cool-enough surface, they condense
back to
a liquid or solid there,” he said. “Over time, they form a thick
layer
of creosote that a hot fire can ignite, causing a dangerous
chimney fire.”
Filling a wood stove at night and closing the damper to
reduce airflow
can keep a fire burning slowly until morning. But it can also
help creosote
to form. So can building little fires just to “knock the chill
off.”
“Burning wood that hasn’t been seasoned long enough favors
creosote
buildup, too,” Beckwith said, “because evaporating water cools
the burning
process.”
