If you burn wood to heat your home you undoubtedly have an interest in choosing woods that are clean-burning and productive in terms of heat produced. You will get the best results and generate more heat per wood volume when burning the highest density (heaviest) wood you can find.
Dense firewood will produce the highest recoverable British Thermal Units (BTUs), but all wood must be "seasoned" for optimum heat production.The seasoning process is simply a matter of allowing the wood to dry in order to lower the moisture content. Dry wood burns more efficiently, with fewer hydrocarbons going up the chimney. It's estimated that even a mildly wet log loses fully 5% of its available energy vs. burning a dry log. When burning a wet log, a considerable amount of energy is spent driving off the water, which reduces efficiency.
The Best Woods to Burn by Species
There are several variable properties in different wood species that affect the chances for sustainable, cleaner heat. The best wood species are hard hardwoods that have dense cells, with green (and dried) weights that are relatively heavy. These species will give out more heat when measured in BTUs than softer woods.
The best burning firewood species:
- Hickory: 25 to 28 million BTUs/cord—density 37 to 58 lbs./cu.ft.
- Oak: 24 to 28 million BTUs/cord—density 37 to 58 lbs./cu.ft
- Black Locust: 27 million BTUs/cord—density 43 lbs./cu.ft.
- Beech: 24 to 27 million BTUs/cord—density 32 to 56 lbs./cu.ft.
- White Ash: 24 million BTUs/cord—density 43 lbs./cu.ft.
By comparison, softwoods such as white pine may generate only about 15 million BTUs/cord.Other woods with acceptable burning characteristics include maple (20 to 25 million BTUs/cord), elm, birch, and cherry (about 20 million BTUs/cord).
Sheer BTU potential is, of course, a big consideration when selecting a wood for burning, but it is not the only one, and it may not be even the most important. In general, heavy, dense woods will always produce more heat than softer, more porous woods. But there other things to keep in mind:
Availability and cost: Hickory is a great wood to burn, but it might be expensive if your region doesn't grow much of it. In some communities, a second-tier wood, like maple, might be a more realistic choice due to sheer availability.
Difficulty of splitting: If you are splitting your own wood for use in a fireplace or woodstove, the splitting characteristics of the wood will make a big difference. Woods with predominantly parallel grains, including oaks, ash, and hard maple are easy to split. Those with interlocking grain, such as elm and sycamore, are notoriously hard to split.
Burning characteristics: All firewood burns in three distinct stages: in the first stage, the wood is being heated to a point that fully drives all moisture out of the cells. In the second stage, actual flames are chemically combining oxygen with carbon to produce flame as the wood is consumed. The third stage, known as "coaling," is when the wood is reduced to glowing embers that radiate a lot of heat.It is this stage, not the flames themselves, that produces the most heat. The ideal wood species for a heating fire are those that pass through the flame stage with a minimum of smoke and ash, and then spend a long time in the coaling stage.By all measures, the five species mentioned above all fall into the excellent category for heat-producing woods, with oak and hickory winning top honors.
information cited from Steve Nix at thoughtco.com