Updated: Oct. 11, 2023
Concerned about creosote? Learn what it is, where you might find it in and around your home and how to stay safe.
What’s in a name? If you’re talking about creosote, it may get confusing. As the Creosote Council explains, many substances are referred to as “creosote.” Here, you’ll learn about the two main types of creosote that you may encounter as a homeowner and what you need to know to stay safe.
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What Is Creosote?
The two main types are coal-tar creosote, used as a wood preservative for industrial purposes like railroads and utility poles, and wood-tar creosote that develops in chimneys from burning wood in a fireplace.
Wood preservative
As a homeowner, you’ll rarely come across this type of creosote because it’s not used for residential purposes. Registered as a pesticide and restricted by the United States Environmental Protection Agency (EPA), it’s not available on the retail market.
According to the EPA, “creosote is derived from the distillation of tar from wood or coal and is used as a wood preservative. Pesticide products containing creosote as the active ingredient are used to protect wood used outdoors [such as railroad ties and utility poles] against termites, fungi, mites and other pests.”
Used for more than 100 years to preserve wood infrastructure, coal-tar creosote often contains chemicals that may be harmful to people. Though it poses cancer and non-cancer health risks to workers in wood treatment facilities, the EPA found no risks of concern to the general public.
The only time you may find creosote in a residential setting, according to the EPA, would be if creosote-treated railroad ties are recycled as landscaping timbers in your yard. If you ever need to dispose of creosote-treated wood materials, it’s critical to check with your local government for specific guidelines.
Chimney residue
Generally, a chimney is the only place a homeowner might encounter creosote.
“Creosote is a sticky, tar-like residue that builds up in chimneys when wood is burned,” says Dan Morris of Fire and Saw. “It forms when the wood doesn’t burn completely and the smoke cools down as it goes up the chimney.”
Condensation occurs as smoke, water vapor, gases, unburned wood particles, hydrocarbons, tar fog and assorted minerals exit the fireplace or wood stove and flow through a much cooler chimney. That process produces the black or brown residue known as creosote that sticks to the inner walls of the chimney.
Should I Worry About Creosote In My Chimney?
If creosote builds up in large quantities and the internal flue temperature is high enough, it could spark a chimney fire. According to the Chimney Safety Institute of America, restricted air supply, unseasoned wood and cooler than normal chimney temperatures can boost creosote buildup.
“Creosote is a known carcinogen, but your average homeowner won’t be exposed to enough to be harmful to any great extent,” Morris says.
Still, creosote can irritate the eyes and skin. When you clean a chimney flue, creosote particles become airborne, and they end up on the brush, in the firebox and anywhere else in the vicinity.
“I brush out our wood stove flue two or three times a year, and I’ve become sensitive to creosote on my arms,” Morris says. “If I don’t cover up, my skin will feel itchy and irritated for several days afterward.
Is Creosote Buildup Normal?
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Yes. Morris says creosote in your chimney or flue is completely normal and the natural consequence of burning wood.
Most creosote formation happens high up the chimney and on the cap/exit kit, so you won’t see it forming in the firebox or near the base. It adheres to the sides of the chimney as the smoke travels farther away from the source of the heat. The longer you go without cleaning your chimney, the more buildup you should expect.
“When a chimney or flue stops drawing so well, this means you need to clean your chimney,” Morris says. “Smoke will come back into the room rather than going up and out.
“Creosote is unlikely to completely close off a chimney, but it can get close to doing so. The chimney cap often has narrower exits that can become very gunked up by creosote.”
What To Do About Creosote Buildup
To avoid a serious issue like a fire, it’s helpful to know when to clean your chimney and how to inspect your fireplace for any signs of trouble.
Additionally, here are some ways to minimize creosote buildup in your chimney or flue:
- Keep the damper fully open while using the stove or fireplace;
- Avoid burning unseasoned wood;
- Don’t burn wet wood;
- Choose hardwoods like oak or maple versus softwoods like pine or spruce with more creosote-forming resins;
- Don’t overload the firebox with wood;
- Have your chimney cleaned and inspected at least once a year. If you’re using the fireplace or stove daily, Morris recommends cleaning it every two to three months.
