October 25, 2021 Lawrence Macmillan

Why Does Firewood Pop?

Is there anything better than lighting up a fire and spending a cozy evening in on a dreary winter’s day?

It’s warm, the dancing flames provide a gentle ambient glow, and the firewood crackles away like a dusty old vinyl record — perfection!

There’s something about that signature crackle coming from the fireplace that really sets the tone of the evening.

It’s almost therapeutic, lifting the stress of the day and setting it aside, so we can truly enjoy the moment.

I mean...there’s a reason Netflix offers endless footage of a roaring fire, popping away.

Even without the warmth of a real blaze, this noise instills a sense of hygge, but have you ever wondered what causes the classic pop of burning firewood?

What Causes The Snap, Crackle, And Pop Of Burning Firewood?

As I’m sure you’re aware, firewood is rarely completely dry. Properly seasoned firewood still contains around 20–25% of its original moisture content. Even kiln dried logs retain roughly 15%.

All this residual water and sap nests itself in a labyrinthine network of microscopic pockets within the firewood.

When we ignite our logs, pour a glass of red wine, and prepare for a lovely evening watching a few movies, the moisture in these tiny pores begins to boil.

Once a substance is heated, the molecules become excitable and start to dance around. They move further and further away from one another, eventually forming steam.

Still trapped in the tiny pockets, as the steam continues to heat up, it exerts more and more pressure on the walls of its woody cell.

Whilst the steam becomes more irritable by the second, its molecules hammering away on the interior edges of these tiny nooks, the fire is weakening the structure of the surrounding wood.

Eventually, the pressure ruptures the structure of the log, and the steam shoots out into the flickering flames of the fire.

It’s this miniature explosion that causes the popping and crackling sound we love so much in a fire.

That signature noise is a combination of the wood reaching breaking point and the steam bursting free from its cage — amazing, right?

Why Does Firewood Spit Embers Into the Room?

Okay, so although these tiny pockets of steam build up some serious pressure, they rarely contain enough energy to throw pieces of wood or embers.

But why then will firewood send a tiny meteor our way every now and again, threatening to blemish the carpet and set our cat’s tail on fire?

The reason for this aggressive reaction to combustion is that logs aren’t only full of very small pockets, they’re also riddled with knots and sizable voids.

These gulfs contain moisture too. When we get a fire going, it heats up just the same as the moisture in the smaller waiting rooms threaded throughout the logs.

Yet, the greater volume of the mixture amounts to a huge amount of pressure when the particles get moving and form steam.

So intense does the pressure become in these recesses that there’s enough energy to cause a rather incendiary reaction, much larger than that of the smaller pockets.

The result is a resounding crack, and on occasion, an artillery-esque firing of debris over an impressively large distance.

This is why it’s essential to invest in a quality fireguard when using an open fire. Failing to block these fiery asteroids will lead to damaged flooring, burns, and potentially even a house fire.

Is Popping Firewood A Good Thing?

The popping sound of firewood may be remarkably euphonious, but, scientifically speaking, it’s a sign of poor combustion efficiency caused by excess moisture within the wood.

What that means is that some of the thermal energy of the fire is allotted to evaporating the residual moisture in the logs, leading to an incomplete burn, more smoke and soot, a dirty stove and chimney, and greater carbon emissions.

The more crackling and popping you hear, the faster your fire will go out, the more wood will waste, and the less heat it will produce.

So, in the same way that lovely popping noise we hear when spinning our favorite records signifies the vinyl is dirty or scuffed, the pleasant pop in our fireplace is an entirely negative phenomenon.

It’s the hallmark of everything we should be trying to avoid when burning wood.

How To Prevent Firewood From Popping

Kiln Dried Wood

The best way to reduce the pop after lighting a fire is to use fully seasoned wood, or better yet, kiln dried wood.

This form of firewood has very little moisture content. It burns efficiently, cleanly, for longer, and will make little to no crackling noises.

Choose Hardwood

Hardwoods have a naturally low moisture content when compared to softwoods, so if you really want to cut the crackle, harvest your wood from elm, oak, ash, walnut, beech, maple, teak, alder, balsa, cherry, hickory, or mahogany trees.

Hardwoods don’t just carry less water than softwoods, they produce less tar and resin, two substances that also contribute to the problematic pop.

Store Your Firewood in a Dry Place with Decent Air Circulation

Wood is a porous material, which means if it gets wet, it’s going to draw the moisture in, so it’s essential you have a dry place to store it.

Here are some pro storage tips…

Store your firewood indoors if at all possible.
If kept outside, make sure it’s lifted at least 2 inches from the floor. This will prevent it from drawing moisture from the ground and attracting insects.
Loosely cover the top of your wood store; a tarp will do. Just try not to have it too close to the top logs, as condensation could form.
Avoid storing your firewood in humid areas.