What is Seasoned Firewood? (Explained)

I sometimes get asked by readers what seasoned firewood is and why they need to use it. I tried finding a guide to send them that explains everything, but I didn’t see a good one out there. So, I put everything together in this article.

Seasoned firewood is wood that has been dried and has a moisture content of 20% or less. This allows it to be stored indefinitely and burn cleaner and hotter. Generally, firewood takes about 6-12 months to naturally season, but commercial kiln operations can dry firewood in as little as 2-3 days.

So, while seasoned firewood is clearly what we should be burning, what qualifies firewood as seasoned, and how long does it take to season? Let’s take a closer look.

Want an easy way to check if your firewood is seasoned? I recommend using a firewood moisture meter. Here’s the moisture meter I use from Amazon.

What Qualifies as Seasoned Firewood

Characteristic	Seasoned Firewood	Unseasoned Firewood
Dry Time	Dried for at least 6 to 12 months	Freshly cut, also called “green” or wet
Moisture %	20% or below	Above 20%
Appearance	Cracks or splits forming	No cracks or splits
Sound	Makes a sharp ring or crack sound	Makes a dull, muffled sound
Storage	Stores indefinitely	Vulnerable to fungus and mold

When a tree is cut, the wood is called green wood. This wood is still wet and full of water, usually having a moisture content of 60% or more. Because of the high amount of water in green wood, it’s difficult to light and burn.

Green wood also contributes significantly more creosote (the harmful tar buildup you see in chimneys).

After cutting and splitting your firewood, it’s important to stack it immediately. This allows the firewood to begin seasoning and losing its water content. For example, if you cut, split, and stack your firewood in the spring, it should be seasoned and ready to use by the winter.

However, some types of wood (such as hardwoods) take longer to season, so aim for a total of 6-12 months of drying time. I’ll cover the best way to season firewood later.

Benefits of Seasoned Wood

• Burns cleaner and hotter
• Lighter (shipping and handling is easier)
• More stable wood
• Machined and cut more easily
• Screws, nails, glue, and other attachments hold better
• Easier to paint and finish
• Risk of decay is minimized

Some of these benefits are for seasoned lumber, but I included them because it helps illustrate the advantages of seasoning.

Other than burning cleaner and hotter, another primary benefit is that seasoned firewood cannot grow mold or fungi.

Since fungi are the only living things that can digest and break down the lignin found in wood, blocking them preserves your firewood.

For example, fungal and mold growth is dramatically slowed at about 30% moisture content and is effectively stopped at 20% moisture content. This is one reason why 20% is the magic number with firewood.

“Wood which has been well seasoned can be stored indefinitely in protected and covered sheds without danger of fungal damage, but green wood cannot”

C. A. Eckeiman, Forestry and Natural Resources, Purdue University

If firewood is infected by mold or fungi, and the wood begins to break down, it begins to have structural problems. It can also absorb about 4 times the amount of water as non-infected firewood.

So, as long as the wood stays dry, it’s immune to degrading from biological sources such as fungi and is great to use as firewood.

Free Water vs Bound Water

Free water is water that is found in the wood cavities and is easily lost. This is the first water to leave green wood and gets the moisture content down to around 30%. Free water leaves the wood similar to a wick.

Bound water is the water held within the wood’s cell walls and takes much longer to dry. The loss of bound water is what gets the firewood below a 30% moisture content and makes it suitable to burn. Much of the bound water is found deeper in the wood, which is why splitting firewood is helpful.

Fiber Saturation Point

When the free water has left the firewood and only the bound water remains, this is the fiber saturation point. It occurs at about 30% moisture content.

The fiber saturation point means that more energy is now required to dry the cell walls (bound water) than the free water. It also means that the wood’s cells now shrink, and structural changes in the wood begin to take place.

Overall, the wood shrinks and becomes more ridged and stronger.

So, the majority of the time needed to season your firewood is due to this process and losing its bound water. Once your firewood has lost its bound water down to at least 20% moisture content, it’s considered seasoned and cannot become unseasoned.

Tip: Seasoned firewood that’s wet or rained on only takes about 1 sunny day to dry.

Hardwood vs Softwood

Softwoods	Hardwoods
Pine	Oak
Cedar	Walnut
Fir	Cherry
Redwood	Birch
Spruce	Poplar
Hemlock	Maple
Larch	Ash

Softwoods are trees that grow fairly quickly and therefore have less time to accumulate water in their wood. While softwoods have a reputation for being poor firewood, they work fine as long as they’re seasoned. Softwoods can contribute to more creosote if they’re not seasoned.

Hardwoods are superior when it comes to firewood (as well as construction) due to the compact and sturdy nature of the wood fibers. This allows them to burn slower and hotter.

Generally, softwoods season faster since they have lower water content. For example, a pine log has an estimated 70 gallons of water while an oak log of similar size contains around 1,050 gallons of water.

Recommended: Can You Burn Pine in a Fireplace? (Answered)

Since hardwoods make better wood and grow slower (oaks and walnuts take 80 years or more to mature), they’re much more valuable.

Heartwood vs Sapwood

Typically the heartwood or center of the tree is drier, while the sapwood or the outer, newer rings are wetter. While sapwood dries fairly quickly, it takes time for it to wick out the remaining water found in the heartwood. Again, this is why splitting firewood is so helpful when seasoning.

How Long Does Wood Take to Season?

Seasoned vs Kiln-Dried Firewood

Air-Dried	Kiln-Dried
6-12 months	2-3 days
Anyone can do	Commercial
Free	More Expensive

The firewood you buy from the store is most likely kiln-dried, which is a large oven that dries the firewood. Kilns operate between 70ºF to 212ºF+, but most conventional kilns are around 110ºF to 180ºF. The typical time to dry green firewood with a kiln is about 2-3 days.

However, few people have or need a kiln.

The best way for the average person to season firewood is to first cut it in the spring, and then split and stack it under a firewood shed. The roof of the shed protects the firewood from most of the rain and snow and allows the sun and wind to speed the seasoning process. This takes about 6-12 months.

Often, the firewood is seasoned and ready by the winter.

The second best way to season firewood is to buy a fireplace rack and cover the top with a tarp. It’s important to not cover the sides as the airflow is necessary to dry the wood. Keeping the wood off of the ground avoids it from soaking up water and rotting from fungi found in the soil.

To see the most affordable and effective firewood racks, check out these firewood racks on Amazon.

Of course, the biggest con to seasoning firewood without a kiln is the amount of time you have to wait. However, this is easily avoided if you cut or buy your firewood at least a year in advance. Many people buy 2-3 years worth of firewood for this reason.

You can also store your firewood in a closed shed or garage, although it takes longer to dry. You can speed this up by using a fan and/or a dehumidifier.

Wood can also be seasoned in covered sheds with a maintained temperature of 110ºF to 120ºF, along with fans to circulate the air. These are also called semi-kilns. In this case, wood can be seasoned in as little as 3 months (with an estimated 8-12% moisture).

To learn more about the benefits of covering firewood, check out my other post: Should Firewood Be Covered? (& The Best Ways)

Tips to Season Firewood Faster

• Split your firewood into quarters – Not only does more surface area mean quicker drying, but the heartwood is exposed, allowing the bound water to escape much more easily.
• Place in a hot or sunny location – If you don’t have a kiln, place the firewood in the sun if possible. An area that is facing south will have the most sun (north if you live in the southern hemisphere).
• Increase air circulation – Like the sun, the wind is a natural drying force and speeds up the seasoning process dramatically.
• Cover your firewood – Especially if you live in the northeast. You’ll gain more by covering your firewood from the rain and the snow than by exposing it to the sun. Again, only cover the top so air can flow through the pile.

For more tips on seasoning firewood, check out my other post: The 10 Fastest Ways to Season Firewood.

How to Tell if Firewood is Seasoned

Here are the top 3 ways to tell if your firewood is seasoned.

1. Moisture Content – Use a moisture meter to tell if your firewood is seasoned with 20% or less moisture content. These meters are fairly inexpensive and easy to use. Here’s the moisture meter I use on Amazon.
2. Visual – Seasoned firewood has large cracks in it from the drying process.
3. Sound – If you bang two seasoned pieces of firewood together, you should hear a sharp ringing sound. Unseasoned firewood sounds like a dull thud (due to the amount of water in the wood absorbing the sound).

Recommended: Firewood vs Firelogs: Which is Better?

For more about seasoning firewood and why split wood is much better, check out this video by Purple Collar Life.

Sources

• https://www.extension.purdue.edu/extmedia/FNR/FNR-155.pdf
• https://www.esf.edu/wus/documents/DryKilnOperatorsManual.pdf
• https://warren.cce.cornell.edu/natural-resources/heating-with-wood/storing-and-drying-firewood

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Should Firewood Be Stored Inside or Outside? (Answered)

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