Heating your home with wood is a practical alternative to high oil and electricity prices. Some people heat completely with wood and some burn wood in addition to their conventional heating system. Either way, knowledge of different woods or how they burn will make the whole process more economical and cost efficient. Different ways to burn wood affect the efficiency as well. Indoor wood stoves, fireplaces and outdoor wood fired furnaces provide varying levels of heat.
A roaring fire in the fireplace gives a beautiful site but not much in the way of heat. Most heat goes up the chimney with only an average of 10% of the available heat making its way into your home. More heat is lost through the open flue after the fire burns down but is not cool enough to handle the damper. The newer generation of wood stoves claim efficiency of 50 to 75% or higher. Outdoor wood fired furnaces are located outside of the home in a contained shed. Water is heated in pipes by the outdoor furnace then pumped back into the home via underground piping. The hot water is circulated through the home heating pipe system. When the water cools down it is pumped back into the outdoor furnace pipes to be heated again. Efficiency levels are low, in the 25 to 50% range. They burn a large amount of wood at a low temperature creating a lot of smoke. State and local regulations restrict use and placement of wood burning appliances. Check with your town’s building or fire marshal for any restrictions and requirements.
The type of wood burned and level of moisture of the wood effect the heat produced. Freshly cut wood contains high levels of moisture. Wood must “season” or dry out for several dry months until the cells release the moisture before burning. The nature of wood combustion is such that the moisture within the wood must be released as steam then the volatile portion of the wood can burn releasing heat. So wet or “green” wood spends too much energy on releasing moisture to make it worth while.
Wood is normally measured and sold in cords. A cord is a pile of wood, bark and air spaces equal to the measurements of four feet high, four feet wide and 8 feet long, or 128 cubic feet. A tightly packed cord of wood will contain more pieces of wood than a loosely pack one. The actual weight of the wood will vary with the moisture content and the type of tree.
Heat is measured in British Thermal Units or BTUs. One BTU is the amount of heat required to raise the temperature of one pound of water one degree F. One pound of any type of wood dried to equal levels will produce the same amount of heat when burned, 8,600 BTUs. The heavier or denser the wood is, the better the heat value. Hard woods like maple and oak will be heavier than soft woods such as pine and fir. Likewise, a cord of hard wood will weigh more than a cord of soft wood. It will take larger amounts of soft wood than hard wood to produce the same amount of BTUs.
Hardwoods are beech, some maples, hickory, locust, ash and oak. Softwoods are pine, spruce, cedar and willow. The soft woods contain more resin which will catch fire faster. These are ideal for kindling.
Store all firewood outdoors a few inches off the ground to prevent moisture from wicking up. Keep the top of the pile dry with the sides open for good air circulation. Fire wood stored inside can bring unwanted insects into your home. Some insects find the split wood a great place to spend the winter until they experience the unexpected warmth of your home and decide it is spring, ending their winter sleep.