There’s more to burning wood than you might expect. Whether you’re using an outdoor fire pit, your fireplace, or a wood burning furnace or stove, different woods burn differently from one another.

And maybe you just buy whatever firewood is available at your local store. But have you ever stopped to ask, “What kind of wood is this, anyway? Do certain types of wood give off more heat than others? What type of wood should I be burning?”

The type of firewood available to you often depends on what kind of trees are native to your area. But, given the choice, some types of wood are better at some things than others. We should know — we’ve been through the process of getting a wood burning furnace approved by the EPA, and that involves dozens of burn tests with many different kinds of firewood.

In this guide (and with the help of data from Utah State University), we’ll cover 10 different species of firewood. We’ll tell you how much heat each species puts off, how much a full cord of each species weighs, and more insights to help you find the right wood to burn.

Firewood BTU Chart

The following chart covers basic information on ten species of wood common in North America. Depending on where you live, some species of firewood may be more readily available in your area than others.

The second column indicates how much energy (in British thermal units, or BTUs) a full cord of each species of wood will radiate when burned.

The third column indicates how much a full cord of each species of wood weighs after it’s been fully seasoned and dried out.

The fourth and fifth columns indicate how easy (or difficult) each type of wood is to split and how much smoke each species of wood tends to give off, respectively.

How Much is a Cord of Wood?

A full cord of stacked firewood measures 4 feet high, 8 feet wide, and 4 feet in depth (for a total of 128 cubic feet). A full cord usually contains between 600 and 800 logs.

You may also see the term “face cord” used; this is about ⅓ of a cord, or 4 feet high, 8 feet wide, and 16 inches in depth.

A half cord of wood measures 4 feet high, 8 feet wide, and 2 feet in depth.

How Long Does it Take to Season Firewood?

The best way to season firewood is to stack it on a log rack and let it sit anywhere from 6 months to a year. This allows moisture to evaporate from the logs.

A piece of firewood may contain up to 50% of its weight or more in water. Waterlogged firewood won’t burn well. The goal is to get the moisture content to 20% or less (and you can test the moisture contents of a piece of firewood by using a moisture meter).

Because it takes so long to season firewood properly, most people buy their firewood a year in advance. When seasoning firewood, leave it outdoors in the open at least a few feet away from walls or other obstructions to facilitate proper airflow. Cover the top with a tarp to keep the wood safe from precipitation (but leave the sides uncovered to allow air to circulate).

Is Oak Good Firewood?

One full cord of dry, properly seasoned oak firewood will put off 29.1 million BTUs of energy, making oak one of the most efficient species of wood to burn. Though it’s heavy (with a full, dry cord weighing in at around 4,200 pounds) and not necessarily easy to split, oak wood puts off relatively little smoke when seasoned correctly.

• Heat per cord (in millions of BTUs): 29.1
• Weight per cord (dry): 4,200 pounds
• Ease of splitting: Medium
• Smoke contents: Low

Is Black Locust Good Firewood?

At 27.9 million BTUs of energy per cord, black locust wood is nearly as efficient as oak. It maintains a comparable weight at about 4,000 pounds per cord. It also puts off relatively little smoke, though it is pretty difficult to split if you’re cutting it on your own.

• Heat per cord (in millions of BTUs): 27.9
• Weight per cord (dry): 4,020 pounds
• Ease of splitting: Difficult
• Smoke contents: Low

Is Maple Good Firewood?

Maple is one of only three species of firewood on this list to put off over 25 million BTUs of energy per cord burned. It’s quite a bit lighter than oak or black locust, averaging about 3,700 pounds per cord. It’s also very easy to split, and it puts off very little smoke.

• Heat per cord (in millions of BTUs): 25.5
• Weight per cord (dry): 3,680 pounds
• Ease of splitting: Easy
• Smoke contents: Low

Is White Ash Good Firewood?

White ash is a great middle-of-the-road firewood option in terms of millions of BTUs per cord at 24.2. A dry, seasoned cord of white ash firewood weighs in at around 3,500 pounds, and it produces relatively little smoke. It’s not the easiest type of firewood to split, though, so keep that in mind if you’re cutting your own wood.

• Heat per cord (in millions of BTUs): 24.2
• Weight per cord (dry): 3,470 pounds
• Ease of splitting: Medium
• Smoke contents: Low

Is Black Walnut Good Firewood?

Black walnut is a relatively efficient firewood, offering about 22.2 million BTUs of energy per cord. It’s pretty light for its efficiency, with a full cord clocking in at around 3,200 pounds. It’s also easy to split, and it puts off very little smoke.

• Heat per cord (in millions of BTUs): 22.2
• Weight per cord (dry): 3,190 pounds
• Ease of splitting: Easy
• Smoke contents: Low

Is Elm Good Firewood?

At about 3,000 pounds per cord and with an energy rating of about 20.9 million BTUs per cord, elm is a good middle-of-the-road firewood. Be cautious, though — it’s pretty difficult to split, and it puts off quite a bit more smoke than oak, black locust, maple, white ash, or black walnut.

• Heat per cord (in millions of BTUs): 20.9
• Weight per cord (dry): 3,020 pounds
• Ease of splitting: Difficult
• Smoke contents: Medium

Is Birch Good Firewood?

Birch’s energy capacity is comparable to elm at 20.8 million BTUs per cord. Its weight per cord is also comparable to elm at around 3,000 pounds. Like elm, it puts off a medium amount of smoke, and while it’s not the easiest wood to split on your own, it is easier than elm.

• Heat per cord (in millions of BTUs): 20.8
• Weight per cord (dry): 2,990 pounds
• Ease of splitting: Medium
• Smoke contents: Medium

Is Douglas-Fir Good Firewood?

Douglas-fir firewood is on par with elm and birch in terms of energy efficiency; it puts off about 20.7 million BTUs per cord. It weighs in at about 2,970 pounds per cord and it’s easy to split. The biggest caveat with douglas-fir is that it probably puts out the highest amount of smoke of any firewood on this list.

• Heat per cord (in millions of BTUs): 20.7
• Weight per cord (dry): 2,970 pounds
• Ease of splitting: Easy
• Smoke contents: High

Is Green Ash Good Firewood?

Though every type of firewood on this list is very efficient, green ash does come in second-to-last at just 20 million BTUs per dry, seasoned cord. It is relatively lightweight; at just 2,880 pounds per cord, it’s about 1,300 pounds lighter than oak. It’s also easy to split and emits a low amount of smoke.

• Heat per cord (in millions of BTUs): 20
• Weight per cord (dry): 2,880 pounds
• Ease of splitting: Easy
• Smoke contents: Low

Is Sycamore Good Firewood?

Sycamore has the unfortunate distinction of being the only firewood on this list not to crack 20 million BTUs per cord, just missing the mark at 19.5. It puts off a medium amount of smoke, too, and it’s relatively difficult to split. It is the lightest, though, with a properly seasoned cord of sycamore weighing about 2,800 pounds.

• Heat per cord (in millions of BTUs): 19.5
• Weight per cord (dry): 2,810 pounds
• Ease of splitting: Difficult
• Smoke contents: Medium

What Type of Firewood Should You Get?

As you can see, there’s more to burning wood than you may have expected. Thermal efficiency can vary by millions of BTUs per cord and weight can vary by thousands of pounds. There are also big variations in how easy each species is to split and how much smoke each species emits.

So — which firewood should you get?

In a lot of cases, this simply depends on which wood is native to your area. You may not have many options.

But, if given the choice, oak, black locust, and maple are high on the list in terms of heat per cord. Green ash and sycamore may be less energy efficient, but they’re very lightweight if you plan on hauling the wood yourself.

Whichever type you choose, be sure to store and season your wood properly. That way it will burn efficiently and cleanly, keeping you warm through the fall and winter months.

It’s easy to get lost in a sea of details when thinking about wood furnaces. People tend to wonder, “How do I know which one to get? When I do find one, how am I going to install it? How do I connect it to my ductwork? How do I clean and maintain it over time?”

And those are all important questions. But perhaps the most important question that you should keep front and center in your head is, “How should I be burning wood in my furnace?”

Wood burning is as much an art as it is a science. We should know; we manufacture an EPA-approved furnace, and the process of getting a wood burning appliance approved by the Environmental Protection Agency includes plenty of burn tests. From the kind of wood you should use to the process of keeping a fire burning, there’s a lot that goes into good burn practices. And that’s exactly what we want to teach you about.

By the end of this guide, you’ll know exactly what you need to do to burn wood in your wood burning furnace the right way. We’ll teach you about moisture content, firewood storage, and starting and maintaining a fire so you can get the best out of your wood furnace.

How to Season Firewood for Your Wood Furnace

Before even putting wood into your furnace, you have to make sure you have the right kind of firewood. In some cases, 50% or more of the weight of a piece of firewood may be water, which doesn’t exactly translate into a good burn.

Firewood burned in a furnace should contain 20% moisture or less — a measurement you can ascertain from a moisture meter. But how can you reduce the amount of moisture in your firewood? The answer is a process called seasoning, and it involves four steps:

1. Splitting firewood
2. Stacking firewood
3. Covering firewood
4. Storing firewood

Splitting Firewood

Picture a cylindrical piece of a tree trunk or branch that’s about 16” high and 12” in diameter. It’s not a good idea to try to burn this piece of wood. It’s too bulky, and it may contain too much moisture. It’s best to split that wood into four (or more) pieces to help it dry out quickly and burn more easily.

In most cases, when you buy firewood it will already be split. But whether you’re buying wood or you plan to split it yourself, you should be looking to wind up with logs that are about 12” to 16” long and about 4” to 6” in width.

Stacking Firewood

The best and most efficient way to organize your firewood is to stack it. But it’s not a good idea to stack firewood on the ground; it will gather moisture, which defeats the purpose of the seasoning process.

Instead, buy (or make) a log rack. They allow you to store firewood neatly, and the bottom of the rack rests a few inches above the ground, preventing moisture from finding its way to the logs you’re trying to season.

Covering Firewood

In order to season your firewood effectively, you need to cover it with either a sheet of metal, some plywood, or a tarp to protect it from rain or snow. This may sound counterintuitive, but it’s best only to cover the top of the logs, leaving the sides uncovered.

Covering the sides of the logs on your rack may actually cause moisture build up on them, slowing the seasoning process. Instead, leave the sides open to promote airflow to your firewood. Also, be sure to angle your cover in such a way that allows precipitation to run off and fall to the ground (instead of pooling on top of the cover).

Storing Firewood

After you’ve split, stacked, and covered your wood, the rest is simply a waiting game. Over time, the moisture will evaporate from the wood, bringing you below the 20% threshold. Then your firewood will be ready to burn.

Generally, there are two types of wood you can season and burn in a furnace: softwoods (like cedar, pine, spruce, or juniper) and hardwoods (like oak, hickory, maple, or birch). The length of time it takes to season each type of wood varies:

• Softwoods need to be stored for at least 6 months
• Hardwoods need to be stored for 12 months or more

Plan accordingly and start seasoning your winter firewood in the spring. The longer the wood is allowed to season, the more cleanly and efficiently it will burn.

How to Start a Fire in Your Wood Furnace

After you have a good supply of well-seasoned firewood whose moisture content is under 20%, you’ll be ready to fire up your wood burning furnace.

If you’ve ever made a campfire, the process of starting a fire in a furnace is similar. Start with some kindling (e.g., dry twigs, newspaper, etc.) and get a small fire going. Starting small allows your furnace’s flue to warm up, which promotes a good draft and helps to alleviate creosote buildup.

As the kindling burns, add some medium-sized pieces of seasoned wood to get the fire growing bigger. It’s helpful to keep the furnace’s door open to allow in a bit of air to get the fire going (or if your furnace has a draft blower, you can turn that on to promote airflow). If you do open the door to allow air in, do not leave the open door unattended.

Keep adding bigger and bigger pieces of seasoned wood until the fire takes hold and encompasses the furnace’s firebox.

How to Maintain a Fire in a Wood Furnace

After you get a fire going and the wood fuel burns up, the fire will inevitably diminish (a process that depends on the size of your furnace’s firebox, the type of wood you use, how well-seasoned it is, how much air is getting to the fire, and other factors). As the flames begin to dim, it’s important to stoke them to make sure the furnace continues to put off heat.

To start with, when adding more wood to the fire, open your furnace door slowly to prevent smoke from spilling out. From there, use appropriate hearth tools (like a shovel or fire poker) to spread the coals around.

Don’t put new firewood directly on top of the coals. Instead, push the coals to the perimeter of the firebox and put new wood in the middle. Doing this will promote better airflow and speed up the combustion process. Put the split end of the firewood (i.e., the end opposite the bark) toward the coals. It will catch fire more easily.

Be sure not to overload the firebox with firewood. If there’s too much wood, the fire will smolder, provide less heat, and create too much smoke due to a lack of airflow. Instead, spread logs out, allowing the oxygen coming into the furnace to move freely and feed the fire. If your fire needs a boost, turn your draft blower on to supply it with a bit more air.

How to Remove Ashes from Your Wood Furnace

Wood burning furnaces come with two doors on the front of them — a larger door that leads to the firebox, and a smaller door that leads to the ash pan. Firewood burned in the firebox disintegrates into ashes, which fall through the grate and into the ash pan. After using your furnace for a while, this ash pan will fill up and need to be cleaned.

Wait for your fire to simmer down a bit, and open the door to the ash pan. Scoop the ashes out, and dump them into a metal container away from flammable material. After closing and sealing the ash pan door, allow the ashes in the metal container to cool off. Be absolutely certain the ashes have cooled off completely before you dispose of them!

Why You Should Follow Good Burn Practices

Wood burning furnaces are complex machines. Like engines, their designs are intricate and intentional, and they rely on a combination of engineering, chemistry, and physics to work their magic. Also like an engine, improper operation of a furnace poses a very real risk of injury or damage to property.

Not following good burn practices can lead to excess smoke in your home, the buildup of ultra-flammable creosote in your chimney flue, or even something as simple (yet dangerous) as a hot coal falling out of the furnace door and starting a fire.

It’s not hard to prevent these dangers, either. Use seasoned wood, be cautious when your furnace’s door is open, and dispose of ashes properly. If you follow good burn practices, you’ll be able to heat your home while keeping everyone in it safe.