How Long Should You Dry Firewood?
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A freshly stacked firewood pile promises many roaring fires, so let's answer the burning question: How long should you dry firewood before using it?
Generally you should dry or “season” firewood for six to 18 months before burning. But Mike Kuhns, a Utah State University professor and extension forester, says that time frame can be too broad to be useful. Luckily there are plenty of ways to narrow that window.
Factors To Consider When Drying Firewood
To get the lowest water content, choose between seasoned vs. kiln-dried wood. Buying pre-dried or kiln-dried firewood is preferable, Kuhns says, “as long as you don’t have to pay a lot more for it.” If you’re buying green wood, which holds plenty of moisture, don’t plan to burn it right away. Water left in firewood boils off when the wood burns, using up some of its heat content and emitting more smoke. Rather, prepare an area where the wood can quickly and properly season.
To get a head start on the drying process, cut and burn dead trees.
“Burning wood from trees that were dead for a while when you cut it is OK,” Kuhns said. “Generally the dead wood will start burning more easily. However, if it has been dead for a long time, it will start to decay, which means less heat.”
Average humidity and temperature
If you’re buying green firewood to save money, do it as early as possible. Firewood seasons the quickest in the spring through the hot days of summer, when the temperature is high and the humidity low. If that’s not possible, you can super-charge the drying process with a homemade firewood kiln. In one of these, wood that would take months to season can be dried in days.
Contrary to popular belief, denser wood doesn’t necessarily have a higher water content, but it typically will take longer to season. The wait might be worth it, though, because denser wood produces about double the amount of heat of a lighter wood.
“Quaking aspen, for example, is a light wood that is 2,160 pounds per cord dry, with heat content of 18.2 million Btus (British thermal units) per cord,” Kuhns says. “On the other hand, white oak is a very dense wood species, with 4,200 pounds per dry cord and heat content of 29.1 million Btus per dry cord. This is almost twice the heat content of aspen.”
Kuhns recommend buying split wood or splitting it yourself. “The sooner you do it and the smaller the pieces the better, though it is usually enough to split a round into two to four pieces,” Kuhns says.
The split pieces let air circulate better. Split wood with one side of bark catches fire more easily than pieces with bark on four sides. Learning how to split firewood safely and efficiently is important for any firewood user.
Stack the wood loosely and off the ground to allow more air circulation, which quickens drying times. Keep the pile covered during rain and throughout the winter months.
How To Test Firewood for Dryness
So how can you tell if your wood is properly seasoned? There are a few simple ways.
The visual test
Look for cracks in the end grain, visible at the front of your wood pile. As wood dries, the ends split, gradually opening wider and wider. Green wood still has a bright color, while aged wood will look dull and gray.
The audio test
Dried wood will sound hollow if you tap on it or drop it on the ground. Green wood lands with a thud.
The weight test
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Less water in the wood lightens the weight, sometimes by as much as half. This chart will tell you how much your seasoned firewood should weigh compared to its greener counterpart.
The electronic test
For utmost accuracy, try a simple moisture meter. Seasoned wood has a moisture content of less than 20 percent.
So, How Long Should You Dry Firewood?
There are too many variables to offer a definitive answer. If you do everything correctly when seasoning the wood — cut it into smaller pieces, stack it loosely off the ground, cover it in the rain and snow, dry it in a warm climate with little humidity — you’ll likely have fine, burnable wood in six to nine months.
But what’s your hurry? Our best advice: Season your wood as long as possible. As long as your wood is seasoning properly and you don’t need to burn it right away, there’s no harm in waiting two, three or even four years. (After four years, the wood may start to decay.) By waiting longer, the moisture level in the wood will continue dropping, making it even more efficient to burn.