The Facts About Chimney Fires: Your Questions Answered

What Causes Chimney Fires?

Most chimney fires are caused by a dirty chimney.

We often get asked, ‘What is the black stuff in my chimney?’ Well, anytime you burn wood, byproducts of combustion are formed, and those byproducts include creosote and soot. This is what you’re seeing – and it’s not good.

Soot needs to be removed from the chimney periodically, but the byproduct of woodburning we’re most concerned with when it comes to chimney fires is creosote.

Here’s why…

When you burn wood, the smoke produced by the fire contains unburned wood particles. The smoke cools as it passes through the chimney, leaving condensation on the walls of the flue lining in the form of creosote.

Creosote is a black or brown residue that can be crusty and flaky, tar-like, drippy and sticky, or shiny and hardened. At first, the buildup may be light and easy to remove. But with each fire you burn in your fireplace, creosote can build up, thicken, and glaze.

Naturally, creosote is corrosive and can damage the flue liner over time, but the real concern is its high flammability. Because creosote is formed from unburned wood particles, all forms of creosote are highly combustible. If the temperature within the flue is right, the creosote inside could ignite and cause a chimney fire.

And if you’re thinking the temperature in the flue would have to get intensely hot for creosote to ignite – think again. Creosote can ignite at temperatures as low as 451 degrees F (for context, a fire in your fireplace can burn in excess of 450 degrees F), and even just an 1/8” buildup of creosote is considered enough to cause a chimney fire.

Now, you may be thinking, ‘Big deal. Aren’t chimneys capable of withstanding a little fire?’ Well, the answer is no. Chimneys are meant to contain smoke, not fire.

In fact, if you have a fire in your chimney, within a matter of seconds or minutes, the tile liner could expand and crack, allowing heat and fire to access the attic, nearby walls, and other combustibles in the home through the brickwork. And that’s how a chimney fire rapidly spreads to become a full-fledged house fire.

But creosote isn’t the only thing responsible for dirtying the chimney and increasing the risk of a dangerous chimney fire…

Flammable blockages caused by birds’ nests and other debris, can also cause a chimney fire. And it’s not uncommon to find nesting materials in a chimney, either. In fact, even though many folks don’t realize it, an uncapped chimney is a welcoming place for birds, raccoons, squirrels, and other critters. These critters bring with them nesting materials, fur, feathers, and feces, all of which can cause a chimney blockage, dirty the flue, and lead to a chimney fire.

Like we said, most chimney fires are preventable. All you must do to prevent dirty chimney-related chimney fires is schedule annual inspections and cleanings as needed, and make sure your chimney is properly capped. Easy as pie.

Where Do Most Chimney Fires Start?

Most chimney fires start inside the flue where there’s either creosote buildup or a flue blockage of some kind. As heat from the fire reaches these flammable materials, the creosote or blockage ignites, starting a chimney fire.

What Are the First Signs of a Chimney Fire? How Can You Tell if You Have an Active Chimney Fire?

Is a chimney fire always obvious? Good question. Chimney fires can burn explosively, making them noisy and dramatic enough to be detected by neighbors and people passing by. But not all chimney fires are obvious.

There are actually two types of chimney fires – the fast burn and the slow burn.

If you have a fast-burning chimney fire:

• You may hear loud popping noises or a low rumbling sound, almost like a freight train or a low-flying airplane.
• You’ll likely have large plumes of black smoke coming up through the top of your chimney, or maybe even sparks spraying out of your chimney top. (No, it’s not normal for sparks to come out of your chimney or for large black clouds of smoke to pour out the chimney top.)
• You may smell an intense, hot smell

If you have a slow-burning chimney fire, you may not know anything is happening. These types of chimney fires don’t get enough air or have enough fuel to be dramatic or visible. That’s why they often go undetected until a chimney inspection. But that doesn’t mean they’re any less dangerous.

They can reach high temperatures and lead to more heat transfer to nearby combustible parts of the house. And ultimately, they have the potential to cause just as much damage (if not more) than their spectacular cousins.

Check out the video below, where our Director of Education, Russ Dimmitt, explains.

Remember, not all chimney fires are obvious. You may even have a fast-burning chimney fire and not know it. We know of at least one fireman who was sent to a home with flames shooting up out of the chimney top. The homeowner was shocked when the firemen showed up because they were completely unaware that they had an active chimney fire. It was the neighbor who called 911.

So, don’t rely on warning signs from your chimney – schedule annual inspections and cleanings as needed, and know you’re doing everything you can to safely enjoy your fireplace.

How Do You Stop a Chimney Fire?

You should never assume that a chimney fire will burn itself out or go out by itself. If you have a chimney fire, you should call 911 and get yourself and your loved ones (pets, too!) out of the home as quickly as possible.

If you are burning wood, you may also want to keep a Chimfex® Chimney Fire Extinguisher on hand. This CSIA-approved product can be used to control the fire until the fire department arrives. Here’s a quick how-to-use guide you can print out and keep with your Chimfex®.

How Do You Prevent Chimney Fires?

#1 Schedule annual chimney inspections and sweepings as needed.

The #1 way to prevent chimney fires is to schedule annual chimney inspections and cleanings as needed. A CSIA-Certified Chimney Sweep® will check for dangerous creosote deposits, flue blockages, and other issues that could increase your chances of having a chimney fire.

And if the flue needs to be cleaned, they’ll have the knowledge, equipment, experience, and products needed to safely remove anything that needs to be removed.

Find a local CSIA-Certified Chimney Sweep® right here.

#2 Burn ONLY dry, properly seasoned firewood.

Wet or green wood is a major contributor to creosote production and buildup. So, simply by burning dry, properly seasoned firewood (and nothing else!) in your fireplace, you’re greatly reducing your chances of having a chimney fire.

For everything you need to know about firewood and what NOT to burn in your fireplace or woodstove, check out the Ultimate Guide to Firewood.

#3 Make sure your chimney is properly lined (and the liner is in good shape).

A good, appropriately sized, and properly installed chimney liner will improve the performance and safety of your fireplace or woodstove, which means less fire risk and less creosote production.

If you aren’t sure if your chimney is lined or if the liner is in good shape or right for your appliance, schedule an inspection with a CSIA-Certified Chimney Sweep®. You can find one in your area right here.

#4 Have a quality chimney cap installed.

A good chimney cap that covers your flue will keep outside debris, animals, birds, nesting materials, and other potential blockages out of your chimney. It’s an affordable investment that can save you a great deal of money in repairs AND protect you against chimney fires. Well worth it.

#5 Make sure your chimney gets adequate air.

A chimney that’s getting adequate air will burn at hotter temperatures and have better draft, which, again, means you’ll see less creosote production. How do you make sure your chimney has enough air?

• Keep the damper fully open when the fireplace is in use
• Keep the fireplace doors open when the fireplace is in use
• Follow manufacturer’s instructions for optimal performance