Whether it’s for primary heat, supplemental heat or a nice fire in the fire pit out back having the proper firewood matters. Here we will discuss moisture content, the drying/seasoning processes, best practices for drying.
Trees contain – or more accurately – absorb tons of water through their roots by method of osmosis, this water travels through the inner xylem tissue through capillary action and is then evaporated through the stomata cells in the leaf. Although the amount can vary greatly depending on the species and time of the year, a living tree will contain approximately 50% moisture content by mass. Thus in order to be efficient for burning this “green” wood must be dried to a lower moisture content, if not, the fire will produce more smoke/emissions and burn at a lower temperature.
If the goal then is to have dry firewood, what is considered dry?
The most common understanding of dry firewood is “seasoned” firewood, but what does this actually mean? While the meaning of “seasoned” varies depending on who you talk to, the best way to understand it is through moisture content. Seasoned firewood does not necessarily mean that it has dried for a year or more, rather it is wood that has dried to a have a moisture content of 20% or less. There are two ways to dry your firewood to a moisture content of 20% or less, the first and most common way of drying firewood is to air dry, the second is to dry the wood in a kiln.
What is air drying firewood, and how long does it take?
Air drying firewood is a process to season firewood by allowing the environment’s natural airflow, heat, and humidity to dry out and reduce the woods moisture content to a level of 20% or less. The time needed to adequately air dry firewood depends greatly on the species of wood, size/thickness of the firewood pieces, airflow, heat, and environment in which the firewood resides in.
For example: oak firewood cut, split and stacked to air dry in Arizona will dry/”season” much quicker than the same wood, and same process in Washington state.
Unfortunately this means there is no standard time that works across the board, however, in the right environment and with the right conditions firewood can dry/”season” to a moisture content of 15%-20% in as little as 3 to 4 months. In situations where the environment or conditions are less than favorable it can take as long as 8 to 12 months. The key to proper air drying is adequate airflow and heat, these are the two most important factors for air drying firewood. This is due to the fact that water dissipates from the wood cells through the process of evaporation until the wood reaches equilibrium with its environment. Once wood reaches equilibrium with its environment, however, it will always be subject to the atmospheric humidity limiting how low of a moisture content it can naturally dry to.
What is kiln dried firewood, and how long does it take?
Kiln dried firewood is firewood that has been dried in a container/chamber where external factors such as airflow, heat, humidity and atmosphere can be controlled in order to achieve a low moisture content. Kiln dried firewood generally has a moisture content of 7%-12% and can be dried in as quick as 4 to 7 days.
So what is the best way to season firewood?
The best way to season firewood is whatever ends up being the most efficient, effective and economical for the individual or operation seeking to season firewood. For some this may be using a kiln, for others it may be through air drying… if air drying, remember AIRFLOW! Contrary to what one may think, stacking firewood on the ground and wrapping it in a tarp in such a way that keeps it “out of the weather” can do more harm than good. It is easy to think that allowing firewood to sit out in the rain will cause it to rot, and while there is truth to that, tarping is much more harmful because covering firewood traps in moisture, greatly restricts airflow, prevents sunlight exposure thus slowing the drying process, if not stopping it.
How can I check the moisture content?
General Tools or Klein Tools make reliable moisture meters that both detect moisture and don’t break the bank; either one of these moisture meters will work well for measuring moisture content in your firewood.
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