How long does it take to season wood?
Winters are long in Alaska, and it’s never too early to start thinking about the heating season. While burning firewood can be a cheaper alternative to heating oil, it also contributes to the air quality problem in the Fairbanks area. This can be addressed by, first of all, burning no wood during inversions when polluted air is trapped in low-lying areas and secondly, burning only dry wood the rest of the time. Burning wet wood produces excess smoke and tiny particles called PM 2.5, which disperse into the air and into our lungs. Dry wood, on the other hand, produces far less PM 2.5. Fully cured wood—with moisture content of 20 percent or less—is not only cleaner but also creates more heat.
How long does that take in this climate? It depends on the species of wood, when you harvest it, how you cut it and how you store it. A few years ago, CCHRC conducted a study that showed wood can dry rapidly over a single summer—no matter when it’s harvested—but takes quite a bit longer over the shoulder seasons or winter. No matter what kind of wood or which method you use, firewood harvested in the fall won’t be fully cured by that winter.
In the study, split wood harvested in the spring took anywhere from six weeks to three months to dry over the summer, depending on the storage method. Split birch and split spruce, for example, dried in just 1.5 months when stored in a wood shed or left uncovered. In general, the fastest way to dry split wood was by storing it in a wood shed or leaving it uncovered, although uncovered wood is at the mercy of the weather and could be wet again by fall. When stored under a tarp, the wood took three months to cure.
Unsplit wood, on the other hand, didn’t cure over the summer no matter how we stored it. Though it neared 20 percent moisture content by the end of the summer, it required another summer to reach a full cure.
Firewood harvested in the fall didn’t cure by springtime regardless of how it was cut or stored. While it dried out somewhat in a wood shed (to between 30 and 40 percent moisture content) some samples actually got wetter under a tarp over the winter.
Several other factors should be considered when seasoning your wood. Spruce and birch tend to dry more quickly than aspen. And your drying times will also vary based on exposure to sun and air circulation (the more, the better).
The good news is that it’s possible to harvest firewood in the spring and cure it over a single summer—so you can get your chainsaw out on a sunny spring day and start prepping for next winter.