Since most firewood is locally produced, the best varieties for fuel vary from region to region. Even though in many homes a fireplace is not the main heat source, correct maintenance and use is always important. Improper fuel can be dangerous and unhealthy as well as inefficient. Selecting the proper wood fuel will involve learning to identify major classes of trees as well as species, and avoiding modern hazards from composites and chemicals.
The primary hazard when using wood burning heating systems is the buildup of flammable creosote on the interior of smoke stacks and chimneys. Resinous woods--from conifers with needles rather than leaves--generate smoke thick with unburned carbon and pitch. Any buildup more than a 1/4-inch thick on the inside of a chimney can catch fire and burn hot enough to crack mortar. Choosing wood that burns cleanly reduces the problem but does not eliminate it totally.
In general, the wood of broad-leafed trees is a safe and efficient fuel for the fireplace. Common species such as oak, hickory, maple and ash are the usual fuel woods in the East and South, with aspen widely used in the Rocky Mountain states. Alder and maple are the most common safe firewood trees in the American Northwest. Choices will always depend on local supply; established dealers know the best species in their area and will not sell inappropriate fuel.
Manufactured fireplace logs, designed for easy starting and even decorative colored flames, are safe to burn but not economical. Bundled camp wood may include a variety of species including pine and cedar. Clean wood scraps often included in bundled wood can make good kindling for starting a fire but should not be used as the primary fuel. Small pieces of wood make a hot fast fire that is difficult to control in an open fireplace; larger pieces burn longer with more radiant coals and less flame.
Scrap lumber may be available for free at construction sites but only clean hardwood lumber is safe fuel. Painted or treated lumber and composites such as particle board contain large quantities of chemicals and should not be burned. Fumes can be dangerous to breathe. In contrast, waste slabs from sawmills can be a practical source of clean, cheap fireplace fuel if you know hardwood by sight.
All firewood should be thoroughly seasoned by storing in a dry location for several months before use. Burning green wood of any species can cause rapid buildup of dangerous layers of creosote and put a home at risk for fire. Regular inspection and cleaning of flues and chimneys is essential.