Firewood Primer
As more and more people are using firewood for heating their homes, I am often asked about differences between hardwoods. Yes, there are differences. There are soft hardwoods and there are hard hardwoods.
In general terms, conifers such as pine, spruce, fir, arborvitae and red cedar are softwoods. They all contain different levels of resins, most often referred to as pitch, which when burnt will create a smoke that can coat the inside walls of the chimney and can cause chimney fires if not properly and frequently cleaned.
However, not all hardwoods are the same with regards to density and the number of BTUs they generate. Soft hardwoods such as tulip poplar, hybrid poplar and tree of heaven are species that burn quickly, as do conifers. But they burn fast and do not sustain fire for long.
Intermediate burning species include red maple, tiger stripe maple and ash.
The wood from elm trees does not burn well and must be mixed with other species when placed in the stove or fireplace.
Oak, beech and hickory are the preferred species for burning because they are plentiful and produce a wood that burns slowly and hot. I have been told by several foresters that a cord of oak or hickory is equivalent to 275 gallons of fuel oil in the amount of heat produced. However, I have not had much luck in verifying this information in the literature. Beech is most often found in firewood sold as mixed hardwood.
Black locust is considered by most seasoned wood burners to be the superior species because it is more dense than oak and generates less ash. However, the densest wood for burning is dogwood, persimmon, apple or pear. A cord of apple or pear is equivalent to 1.5 cords of oak in BTUs generated. The problem in obtaining these as firewood is that dogwood and persimmon trees tend to be small and in limited quantities. Unless you can acquire an abandoned orchard, finding a cord of apple or pear wood to burn is nearly impossible. If you can ever purchase a cord of apple or pear firewood for the price of oak, buy it immediately because you will get more heat for the buck.
Two tree species that you seldom see as firewood are sweet gum and sour gum. Although both species are plentiful in the forest, they are difficult to split even with a log splitter. Both species burn well but are difficult to ignite.
The woods of peach, nectarines, prunes and cherries are not recommended for fulltime burning because they also contain resins that can cause chimney problems.
Ask Dr. Gouin your questions at [email protected]. All questions will appear in Bay Weekly. Please include your name and address.