WOOD
CHARACTERISTICS

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 heating fuel.

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. wpe198.jpg (4193 bytes)

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 of volume.

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.

Wood Characteristics
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.

Wood Selection
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
Drying
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.
Precautions
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.