What Kinds of Wood Can I Split?
Understanding the Janka Scale
Just like you, I dream of quiet nights by a fire. There simply is no substitute for an evening in front of the fireplace with a loved one, or a night around a campfire with friends.
To get firewood for an amazing bonfire, you need the best log splitter.
Besides the length and diameter of the log you’re splitting, your choice of a log splitter depends on other factors:
- Type of wood
- Wood density (how far apart the growth rings are)
- Greenness and moisture content
Because of all these factors, one type of firewood might be denser and harder to split than others.
We have a way of measuring how hard and dense different kinds of wood are: the Janka hardness scale, which makes it easier to pick the right log splitter tonnage for the wood you plan to split.
Why Does the Type of Wood Matter?
The answer involves a little bit of science and a little bit of wood-seasoning know-how.
Certain types of trees produce more sap and retain less water than others. A walk in a pine forest will show you that pine trees, for example, produce a lot of sap, which doesn’t leave a lot of room for water.
Because pine lumber has a low moisture content, its spaces fill with air as the wood dries out during seasoning. This makes the wood less dense and easier to split.
It’s why pine and other cone-bearing trees are considered softwood.
The quality of the wood fibers that remain after lumber has been seasoned also affects hardness. No need to get too deep into the science; just know that certain trees produce a lot of a woody polymer called lignin that strengthens the walls of their cells.
The more lignin a tree’s cells contain, the closer that tree comes to hardwood.
All of it together shows why, when it comes to choosing a log splitter by tonnage, there’s much more than size that matters.
What Is the Janka Hardness Test?
Talking about lignin and moisture content helps only so much. The Janka scale describes the hardness and density of different kinds of wood in a way that's easier for people with firewood to split to understand: with numbers.
Gabriel Janka, an Austrian researcher who worked at the U.S. Department of Agriculture, developed his lumber test and rating scale in 1906. The test was simple but standardized. It measured how much force it took to embed a steel ball 0.444” (11.28 mm) in diameter halfway into a plank of wood at least 2” by 2” by 6” in size.
The denser the wood, the more pressure it took to embed the ball.
Researchers have noted that the direction of the wood grain affects results. Embedding the ball into the plank’s smooth surface perpendicular to wood grain is known as a test of side hardness. In contrast, pressing the ball into either end of the plank is known as a test of end hardness.
Although the steps for testing wood hardness are standardized, the way of reporting the results is not. Today, the United States measures pressure in the Janka hardness test in pounds-force. Sweden, however, uses kilograms-force, while Australia uses a unit called the newton.
In the U.S., the Janka rating goes from 0 to 4000 pounds-force. The lower the number, the softer the wood.
That’s the number you need to know when choosing your log splitter.
How Do I Use the Janka Scale?
A quick Internet search for “Janka scale” will get you a list of trees growing commonly in the U.S. along with a Janka rating for each tree’s lumber, like this:
That’s helpful for understanding which woods are denser and more difficult to split, or softer and easier to gouge and scratch. But those numbers don’t translate easily into log splitter tonnage.
Remember, the right log splitter tonnage depends on two factors:
- The wood’s hardness on the Janka scale
- The diameter of the log being split
A chart that assesses both of those factors would be a helpful, useful way to interpret the Janka hardness test.
Good thing such a chart exists.
Log Splitter Tonnage Chart
(Note: the tonnage values above are different for greenwood vs seasoned wood. You will need 50-75% more tonnage for splitting green wood.)
One important point you might realize after studying this chart: if you have a large log, but it’s cut from a softer wood, you might not need as high a tonnage or as powerful a log splitter as you think.
On the other hand, a small piece of a dense hardwood might require a little more power to split.
You'll see a lot of variety in the diameter of the logs you split from one type of tree to the next. While the trunks of red maple trees tend to be 18" to 30" across at maturity, for example, the trunks of ponderosa pines can grow over 48" in diameter.
However, some of your logs might actually be smaller branches from those larger softwood trees, which a less powerful log splitter can easily handle.
Also, the grain of the wood can affect how easily it splits. Often, woods that have a straight grain (like red oak) are easier to split than woods with a spiral grain (like sweetgum). You might even notice some variety within a species because of this; for example, some people find red oak easier to split than white oak.
All of that variety might make it seem difficult to choose the right log splitter. Based on this chart, though, it's easy to get ideas of which splitters are best for certain kinds of logs. For example:
- A small log splitter (like a 7-ton) for a 6" pine log
- A mid-sized log splitter (like a 22-ton) for a 12" maple log
- A large log splitter (like a 37-ton) for a 36" oak log
A Tool that Fits the Firewood
It's always helpful to plan ahead. Take a look at the trees on your property. If you think you might be splitting larger logs in the future than you are now, it's better to buy the more power splitter ahead of time than to be stuck with the wrong tool.
That being said, no one wants to spend more money than they have to, even on the necessary equipment. Choosing the most powerful log splitter to split nothing more than small pieces of softwood will only burn through your cash.
However, choosing a smaller, less powerful splitter when hardwoods are common in your area will have you burning through your time as you wait for your splitter to get the job done.
The best way to get warm is to sit by a toasty fire. The Janka hardness scale can help you make sure that you have the right log splitter to split all the firewood you need.