The Facts About Chimney Fires: Your Questions Answered
Most chimney fires are preventable, and in this resource, we’re going to help you understand how to prevent them. We’ll answer questions like:
- What causes chimney fires?
- How do you know if you’ve had a chimney fire?
- What should you do if you’ve had a chimney fire?
- And more.
Our goal is to provide you with the knowledge you need to make informed decisions around chimney maintenance and use, so you never have to experience a chimney fire first-hand. So, let’s get started.
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.
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.
How Bad Is a Chimney Fire and Why Is a Chimney Fire Dangerous?
So, what makes a chimney fire so dangerous and how bad is it?
Chimney fires are dangerous because they can rapidly spread to other areas of the home, putting those within the home at risk of injury or death. Not only that, but they can cause a lot of damage to the chimney itself.
Here’s a snapshot of the kinds of damage chimney fires can cause to your chimney, depending on which type you have:
- Masonry Chimneys – When a chimney fire occurs in a masonry chimney – whether the flue is an older, unlined type or tile lined to meet current safety codes – the high temperatures at which the fire burns (around 2000 degrees F) can melt mortar, crack tiles, cause liners to collapse, and damage the outer masonry material. Most often, thermal shock occurs, tiles crack, and mortar is displaced. All this damage provides a pathway for flames to reach the combustible wood framing of the home, which is extremely dangerous.
- Prefabricated/Factory-Built Metal Chimneys – In most jurisdictions in the U.S., metal factory-built chimneys that are designed to vent wood-burning stoves or prefab metal fireplaces must pass special tests or they can’t be installed. Most tests require the chimney to withstand flue temperatures up to 2100 degrees F, without sustaining damage. Even still, if there’s a chimney fire, these systems can be damaged. And unfortunately, when prefabricated, factory-built chimneys are damaged by a chimney fire, they must be replaced.
- Woodstoves – Woodstoves are made to contain hot fires. The connector pipes that run from stove to chimney, however, aren’t. They can’t withstand the high temperatures produced during a chimney fire and will warp, buckle, or even separate from the appliance and chimney because of the vibrations of air turbulence during a chimney fire. If a separation does occur, fire, heat, and smoke can transfer to other areas of the home. Additionally, like prefab chimneys, if the connector pipes on a woodstove are damaged, they must be replaced.
Another consideration is what a chimney fire can do to the home if it spreads. A rapidly spreading fire can cause extensive damage to walls, ceilings, attics, framing, and furniture. All those repair and replacement costs can add up quickly.
When you consider that a chimney sweeping and inspection cost around $150-450 and could potentially save you thousands or even tens of thousands of dollars in repairs, the smart choice is obvious: schedule routine inspections and cleanings for your chimney system.
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.
At What Temperature Does a Chimney Fire Start? How Hot Do Chimney Fires Get?
As we mentioned a little bit earlier, creosote has the potential to ignite at around 451 degrees F. Given that fires in fireplaces can reach temps exceeding 450 degrees F, it doesn’t take a miracle for creosote to reach the right temperature for a chimney fire.
Once a chimney fire is going, it can burn up to 2000 degrees F, which is hot enough to break and crack clay flue tiles and melt metal flue liners in mere moments. That’s why a small chimney fire can become a house fire in very little time.
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 detected 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.
What Should You Do If Your Chimney Is on Fire?
If you have an active chimney fire, get everyone out of the home (and a safe distance from the home) and call 911. A chimney fire can spread to other areas of the home quickly, and you need to get the fire department on the premises ASAP.
The average response time for a fire company is five minutes, although in rural areas, that may be as high as 15 minutes. A lot can happen in that time where fire’s involved, so the sooner you call 911, the better.
And if you can, close all the doors behind you when you leave the house. You want to cut off as much air to the fire as you can to prevent spreading before the fire department arrives.
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 Can You Tell if You’ve Had a Chimney Fire?
Okay, but how do you know if you’ve had a chimney fire? Are there signs you can look for? Yes! There are nine signs you’ve had a chimney fire – these are the nine signs a CSIA-Certified Chimney Sweep® is going to check for during your annual inspection:
- “Puffy” or “honey combed” creosote in your chimney and/or fireplace
- Discolored and/or distorted rain cap/chimney cap
- Warped metal on the damper, smoke chamber connector pipe, or factory-built metal chimney
- Evidence of smoke escaping through the mortar joints of masonry or tile liners
- Cracked or collapsed flue tiles, or tiles with large chunks missing
- Heat-damaged TV antenna attached to the chimney
- Creosote flakes and pieces on the roof or ground
- Roofing material damage from hot creosote
- Cracks in the exterior masonry
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
Join Us on Our Mission to Eliminate Chimney Fires
Chimney fires contribute to millions of dollars in property damage, hundreds of injuries, and several deaths every year. But most chimney fires are preventable. Do your part to reduce your risk by taking great care of your chimney and fireplace and investing in routine services, like inspections, cleanings, and repairs when needed.
We want to continue to see a decline in chimney fires – join us on our mission to get the number of chimney fires down to zero, won’t you?
Want to know even more about chimney fires? Grab our free report right here.