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.
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.