|Fireplaces and wood stoves, popular aesthetic
accessories of the recent past, are rapidly gaining prominence as primary or supplemental
heat sources for homes. The rising costs, and in some instances, actual shortages of
conventional home heating energies have led to greatly increased utilization of wood as a
Firewood, one of nature's most
common methods of storing solar energy, is a renewable energy source. It is a relatively
clean, efficient, safe energy source having low sulfur content and is generally found
throughout the country. Its primary products of combustion are carbon dioxide, water vapor
and ash. The ash content is low--only one to two percent by weight--and that which does
remain can be used as a worthwhile soil conditioner.
|A wood fire is easy to start and produces a large quantity
of heat in a short time as well as adding a cheerful atmosphere to the home. An ample air
supply to the wood fire is important to ensure complete burning or combustible gases. Wood
fires are ideal where heat is required only occasionally, for warming a living area on
cool days or for supplying extra heat in extremely cold weather. When considering wood as
a primary heat source, several factors must be carefully weighed to ensure satisfactory
results and acceptable deficiencies.
The heat content of any fire depends on wood density,
resin, ash and moisture. A rule of thumb often used for estimating heat value of firewood
is: "One cord of well-seasoned hardwood (weighing approximately two tons) burned in
an airtight, draft-controlled wood stove with a 55-65% efficiency is equivalent to
approximately 175 gallons of #2 fuel oil or 225 therms of natural gas consumed in normal
furnaces having 65-75% efficiencies." Generally, hardwoods which provide long-burning
fires contain the greatest total heating value per unit of volume. Softwoods which gives a
fastburning, cracking blaze are less dense and contain less total heating value per unit
All woods dried to the same moisture content contain
approximately the same heat value per pound--from 8,000 to 9,500 BTU for fully dried wood
and 5,500 to 8,500 BTU for air-seasoned wood.
When considering the type of wood for use as firewood, several characteristics are
important. These include heat value, ease of splitting, weight per volume unit, ease of
starting, amount of smoking and coaling qualities. Moisture content of the wood, number of
knots and pitch content affect these characteristics of the more common woods used as
Firewood can be sold by weight. Freshly cut or green wood can contain from 40 to 60%
moisture by weight, whereas properly seasoned wood contains only 15 to 20%. Select the
driest wood when buying by weight. Green wood will shrink approximately 8% in volume (i.e.
10 cubit feet per cord) when properly seasoned.
Firewood / Preparation
Wood should be dried as much as possible before burning. Properly seasoned wood has about
7,700 BTU maximum usable energy per pound versus only about 5,000 BTU available from green
wood. For best results, season or air-dry wood for at least six to eight months after
cutting. This should bring the moisture content down to 15 to 20% by weight. The best time
to cut wood is during the winter or early spring before the sap runs. If the tree is
felled when fully leafed out, let it lie until leaves have become crisp to allow leaves to
draw out as much moisture as possible from the tree before further cutting.
Drying time is greatly reduced if wood is cut into firewood length and split, especially
pieces larger than 8 inches in diameter. Splitting is easiest when wood is frozen or green
and should be done before wood is stacked. Wood must be properly stacked for satisfactory
drying. The greater the surface area exposed to air, the more rapid the drying. Therefore,
stack wood loosely and keep it off moist ground. The stack should be located in an open
area for good air circulation--avoid stacking in wood lots for seasoning.
Storage of Wood
Store firewood outdoors, under partial or full protection from the elements, and no closer
than 25 feet from the house. Keep area around wood clear of weeds, leaves, debris, etc.,
to discourage rodents, snakes, insects, and other unwanted pests from making their home in
the stacked wood. Avoid storing large quantities in the house, warm garage or basement
because the heat will activate insect and fungi or spore activity and bring about hatching
of any insect eggs in or on the wood.
Building a Fire
Before lighting a fire, make sure the thermostat is turned down so air heated by the
central furnace will not go up the chimney. The easiest and best fire for either a stove
or fireplace is achieved with a mixture of softwoods for easy igniting with hardwoods for
longer burning and good coaling qualities. A cardinal rule of fireplace management is to
keep a thick bed for glowing coals that drop through. The coals yield a steady heat and
aid in igniting fresh fuel as it is added. Keep the fire burning by adding small amounts
of wood at regular intervals. A small, hot fire is much better than a large, roaring blaze
because it burns more completely and produces less creosote.
Coal should never be burned in a stove or heater designed for wood. Artificial or
manufactured logs, which are composites of sawdust, chips, colorful chemicals, starch
binders and wax should be burned only in open brick fireplaces. The wax burns at too hot a
temperature for metal stoves and chimneys. When using manufactured logs in fireplaces,
never crumble the burning log with tongs or poker. Avoid using wood salvaged from poles,
posts, and lumber that has been treated with wood preservatives such as creosote or
pentachlorophenol. These chemical compounds may vaporize upon combustion and cause
respiratory problems for those breathing the fumes.
Wet, green wood, or highly resinous wood should not be burned because of the large amounts
of wood tars, creosote and wood extractives given off which can coat chimney flues and
cause serious chimney fires if ignited.