Best firewood bargains may not be cheap
Getting the most heating value per firewood dollar isn't as simple as buying the cheapest cord available. Buyers need to know what to look for and ask about, said Charles Barden, forester with Kansas State University Research and Extension.
"A big point of confusion is that a cord is a measure of volume -- 128 cubic feet. On the other hand, heating value ties directly to wood density -- its weight," Barden said. "You have to understand this difference to know why an expensive cord of wood can sometimes be a bargain."
Cords of wood may look different -- some taller, some wider, some squared-up, some not. Even so, once those cords are well-stacked, multiplying their height by their width and depth will always yield the same answer. The total volume of every honest cord basically fills up an identical amount of space.
Despite that, however, cords can have widely differing weights. And, the heavier (denser) they are, the more heating value they have per cubic foot.
That's why a cord of oak -- considered a premium firewood -- will always cost more than a cord of cottonwood, Barden said. They'll be the same size. But, the oak cord will weigh more than twice as much as the cottonwood, so offer that much more heating value.
"Looked at the opposite way, a ton of cottonwood will provide the exact same heating value as a ton of oak. But, it takes a lot more cottonwood to add up to a ton," he said. "Of course, that only holds true if the wood has been seasoned for at least six months, as recommended. Fresh-cut cottonwood can actually be heavier than seasoned oak, because of all the water that green cottonwood logs still contain."
To complicate things further, some dealers only sell cords of "mixed hardwoods."
"If you hear 'mixed,' you really need to start asking questions," Barden said. "If a mixed cord contains mostly locust, hackberry and ash, it's got plenty of heat value. If it's mostly silver maple, elm and cottonwood, it had better be fairly cheap, because you'll need lots. If it's hedge, hickory and oak, that's really good wood. Both hedge and hickory are actually denser than oak."