Dear Science: I’m buying firewood for the winter. Some dealers sell by the cord, some by the truck load. Some sell pine, piñon, aspen or cottonwood. Others sell mixtures. Prices seem to vary widely. How do I make sense of all this? – Buck R.
Dear Buck: Buying firewood can be a confusing business, to be sure. The short answer is that you should ask your neighbors and friends who have purchased firewood in your region for several years for the names of dealers who sell wood at a reasonable price.
If you don’t have neighbors or friends, you have a different problem. The only standardized measure for firewood is a cord. A cord is 128 cubic feet of wood cut to stove length, split and tightly stacked. To determine the number of cubic feet in a collection of tightly stacked wood, just multiply the length by the width by the height of the stack. For example, a tight stack measuring 4 feet by 4 feet by 8 feet is a cord. When you buy wood by the cord, be sure your dealer means exactly that — 128 cubic feet, tightly stacked. It is against New Mexico law to represent anything less as a cord.
A “truckload” is a meaningless term; in some states, it is even against the law to use the term when selling firewood. As a consequence, there is much room for mischief when wood is sold by the truckload. However, there are some rules of thumb you can use to estimate how much is in a “truckload.” Standard Ford F-150 and F-250 pickup beds (not the “sport” truck and typically not the “extended cab,” either) hold almost exactly half a cord, tightly stacked to the top of the bed. Short-bed pickups typically hold one-third of a cord. Remember, a collection of wood that is loosely stacked can contain as little as half that of a tightly-stacked one, for the same stack length, width, and height.
Firewood that is ready to burn should contain no more than 20 percent water by weight. If the wood contains more water than that, up to a third of the heat produced by burning it is wasted driving out water, not heating your living space. Wet wood also tends to coat your chimney with combustibles that can cause a chimney fire far faster than dry wood does. So how can you estimate the water content of wood? Compare the weight of a piece of wood you know is dry with a piece of wood of similar size whose water content you don’t know. The unknown piece should weigh the same or only a little more than the dry piece.
How do the costs of different kinds of wood compare? Pine/spruce, piñon, aspen and cottonwood are the most commonly available firewoods in Northern New Mexico. Per cord, piñon produces about 50 percent more heat than pine and aspen, and pine in turn produces about 50 percent more heat than cottonwood. These facts can guide your comparison shopping. For example, if a cord of piñon costs less than 1.5 times that of a cord of pine, the piñon is a better buy. If the cost of a cord of pine is less than 1.5 times that of a cord of cottonwood, the pine is a better buy.
It’s essentially impossible to determine whether a mixture of woods is competitively priced because there is no standard for a “mix”.
It may be worth your time to look at less traditional sources of fuel for your wood stove. If you live near a sawmill, you may be able to procure mill scraps at a price well below that of conventional split firewood. In addition, construction companies often generate large quantities of waste lumber; it burns fast, but you can often get it for free if you supply your own transportation. And don’t overlook wooden shipping palettes — they are often made of oak, which has a heat value per cord about twice that of pine. (You will obviously have to saw the palettes into pieces to fit your stove and avoid hitting any nails in the process.)
For more information, contact a reputable firewood dealer or see www.oregon.gov/ODA/MSD/fuel_facts.shtml.
Jack Horner is an independent researcher.