Why does wood pop when it burns?
Firewood pops, crackles, and hisses when it burns due to the moisture inside the wood. As the wood heats up, the moisture inside the wood turns into steam and causes the wood to expand. When the steam is finally able to escape through the surface of the wood, it causes a popping sound.
Other factors, such as age, dryness, and type of wood, are also important when answering the question.
Let’s go through what makes wood pop and some other interesting details.
Why Do Fires Pop?
So, why does firewood pop?
Fires, at their core, are a chemical reaction sped up by high heat levels.
The reaction utilizes a fuel, in this case, wood, and the oxygen in the air to create a heat-producing reaction. The reaction releases energy (heat) by breaking the bonds between molecules, which makes the solid wood turn into gaseous smoke.
As the wood heats up, steam and other gasses begin forming inside the layers of cellulose. Once the fire achieves a certain heat level, the cellulose trapping the gasses begins to break down. Once the cellulose breaks down enough, the gasses escape, creating a popping noise.
There’s nothing abnormal about wood popping or crackling when it burns, although frequent popping can indicate you haven’t dried your wood correctly. Seasoning your wood is essential for a safe, warm, long-lasting fire.
Seasoned Firewood is Essential
Using seasoned wood reduces crackling to a minimum.
Not only does seasoned wood reduce popping, but it’s cleaner, less smoky, and better for your chimney.
You should dry seasoned wood for at least a year before you use it in a fire. Allowing it to dry for a year or so forces the moisture trapped in the cellulose to escape. With less moisture in the wood, your fires will pop less.
But getting rid of popping noises is the smallest benefit of using seasoned wood. Wet wood causes much more smoke. If you’re using the wood indoors, smoke from moist wood can cause a dangerous build-up of creosote in your chimney.
Seasoned wood also burns hotter, meaning you won’t need to burn as much to receive the same heat. Seasoned wood is easier to split and carry into your house, too.
Can Popping Wood Be Dangerous?
Although popping wood is normal, it can cause some problems.
As the steam and other gas escape from the cellulose, the popping sound isn’t the only reaction. As steam releases from the wood, it can also eject embers from the fireplace.
If you’re monitoring your fire, those embers shouldn’t be a problem. But if you leave your fire unattended, these embers can cause a house fire. That’s just another reason to always monitor your fire and keep it safe.
Is Popping Wood Different From Crackling Wood?
No, people use these two terms interchangeably.
Some people prefer to call a fire crackling because it carries more positive connotations. A popping fire sounds like a fire that spits embers, whereas a crackling fire sounds like a nice evening fire during a cold winter.
Do Some Types of Wood Pop More than Others?
Yes, the type of wood you use can increase or decrease how much your fire pops.
The main difference is how much moisture and sap a wood species contains. Let’s go through some common firewood types and answer ‘why does a fire crackle?’
Oak is one of the most popular types of firewood in the US.
Oak grows all across America, with species in 47 states! Oak is a hardwood that burns slowly and evenly when seasoned correctly. For its weight, oak produces a significant amount of heat.
When seasoned properly, oak fires pop less than most other types of firewood. Oak doesn’t have nearly the same amount of tar, sap, or moisture trapped inside. Without those elements, less gas accumulates inside the layers, which means fewer pops.
Beech is another hardwood that people often use as firewood.
Beech grows in the eastern half of America. Beech burns slowly and doesn’t produce a significant amount of smoke. On top of that, beech produces high heat levels.
Just like oak, beech is a great firewood because it doesn’t pop too much. Beech doesn’t contain high amounts of moisture or sap. Without those liquids trapped in the wood, beech doesn’t create the gasses that cause the crackling noises.
Although not commonly used as much as oak or beech, birch is wonderful firewood if you can get your hands on it.
Birch is a hardwood that grows in the eastern half of the US. Like other hardwoods, birch produces a significant amount of heat.
Birch has a low moisture content. Since it has a low moisture content, birch won’t smoke nearly as much as other types. Another benefit of the low moisture content is reduced popping noises.
Ash is among the best firewood because it burns slowly and evenly.
Ash grows in the eastern half of the US, sometimes reaching as far west as Texas. It burns cleanly and creates almost as much heat as oak or birch.
Ash, like other hardwoods, has a low moisture and sap content. It produces few sparks and only pops infrequently.
Cedar is a common firewood used in camping or other outdoor activities, especially in the western part of the US.
There are a few species of cedar in North America, and they grow in almost every state.
But cedar is a softwood. Softwoods aren’t ideal for fires, particularly indoor fires. Softwoods have a much higher moisture and sap content than hardwoods. The high moisture content causes large amounts of smoke and frequent popping from the escaping gasses.
Elm isn’t the most popular option for firewood, but nonetheless, some people use it.
People consider elm a softwood, although it shares some characteristics with hardwoods, too. Elm trees grow in the eastern half of the USA, and some species reach as far as Texas.
Although elm doesn’t have moisture levels as high as cedar or pine, it isn’t an ideal firewood. It produces a moderate amount of smoke. Due to the sap and other moisture trapped inside, elm also crackles a lot, even when dried.
Pine is one of the most common trees in North America.
Pines grow in regions as diverse as New England, Florida, and the Rocky Mountains. But pine is a softwood that most people avoid when looking for firewood.
Pine isn’t ideal firewood because of it burns quickly and doesn’t put out a lot of heat. Also, even when dried for a year, pine produces a high amount of smoke. Not only that, but pine crackles more than any other wood we’ve tried.
Pine cones, on the other hand, are excellent fire starters.
Popping Firewood FAQs
Popping firewood can bring up a lot of questions, so here are the answers to some of the most common questions about it.
What types of wood pop the most?
Of the common species found in the USA, cedar, pine, and fir pop the most.
All of these trees are softwoods, meaning they contain higher moisture levels than hardwoods like oak. Those moisture levels contribute to increased popping when the moisture escapes during burning.
Use a wood moisture meter to test whether or not firewood is ready to burn.
How do you stop firewood from popping?
Once you start burning the wood, there’s no way to stop excessive popping aside from putting the fire out. Although popping may annoy you, it’s no reason to put out your fire and waste the logs.
The best way to stop firewood from popping too much is to prevent it from ever happening. The best way to reduce popping to a minimum is to properly season your wood. By reducing the moisture in the wood, you should get rid of most of the popping noises.
Does popping firewood indicate something worse?
Usually, crackling or popping noises coming from your fire are completely normal. They don’t indicate anything other than how much moisture was left in your logs after you seasoned them.
But in some rare cases, excessive popping can indicate a large release of gas is coming. Under normal circumstances, there isn’t anything to worry about. But if you don’t split your logs, you can cause yourself some real harm.
If you don’t split your logs, seasoning them won’t get rid of the majority of the moisture. Instead, the outer layers will be dry, but the inside will still be wet. As the log heats up, the moisture in the middle will begin to turn to gas.
As the gas builds up, it looks for an area where it can escape. If the log isn’t split, it has nowhere to go. The gas can then build pressure to dangerous levels, causing the log to break apart. It can send embers and other debris flyings several feet.
So, why does wood pop when it burns?
Wood pops due to the build-up of gasses inside the wood. As those gasses escape, they cause small popping or crackling noises.
Choosing a hardwood species and seasoning it for an appropriate amount of time will reduce how often your fire pops. As long as you dry your wood correctly, these popping noises are nothing to worry about.