The Three Degrees of Creosote
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Three Degrees of Creosote

creosote build up

How Dangerous is the Creosote in Your Chimney?

Did you know that not all creosote is the same? The wood-burning byproducts consisting of a mix of tar, creosote, and soot, which build up in your chimney lining every time you burn a fire, have three degrees or stages. The third degree is the most dangerous, but all types of creosote are highly flammable and could start a chimney fire. One of the most important reasons to get an annual chimney inspection and cleaning is to remove the creosote. How easy or difficult it is to remove depends on which form of combustion byproducts is inside your chimney.

1st Degree

The first degree of creosote is composed largely of soot and can be easily removed using a basic chimney brush. This is definitely the type of creosote you want the chimney sweep to find in your chimney, and in large part, it’s up to you whether it is.

When seasoned wood is burned, fire gets the needed air, and the heat of the fire warms the flue, first-degree creosote is what is produced. Seasoned wood has low moisture content and produces good combustion, meaning that wood components are burned up rather than going up the chimney.

If the flue doesn’t warm properly, giving you ideal conditions for first-degree creosote, it could be because your house is sealed too slightly, preventing a proper draft in the chimney.

2nd Degree

Second-degree creosote looks like shiny black flakes. It is usually produced when the air is restricted, and wood stoves and fireplaces that have glass doors commonly cause this.

The flakes of second-degree creosote contain hardened tar, and this combustion by-product does not brush away easily. It’s important to remove the creosote because of the potential for a dangerous chimney fire.

A rotary loop is what is most often used for the removal of second-degree creosote. The equipment consists of a stainless steel cable attached to a hub, which has metal rods that are turned by a powerful drill. What often happens when a rotary loop is used is that pre-existing damage in the liner becomes evident because loose pieces are knocked down the chimney. Homeowners often think the rotary loop caused the damage, but it’s not the case.

3rd DegreeThird-Degree Creosote

Third degree creosote looks like tar coating or running down the inside of the chimney, and it is extremely flammable. The creosote hardens and is repeatedly recoated when the fireplace or wood stove is used. If the creosote in the liner catches fire, third degree creosote sometimes burns up, leaving a lightweight “sponge” that is simple to remove; but a chimney fire is very dangerous and the creosote usually does not burn up. There are chemicals that do a fair job of removing third degree creosote, but the best course of action is often to replace the chimney liner. The following are some conditions that cause this problematic buildup:

  • Burning unseasoned firewood
  • The flue is oversized
  • An insufficient amount of combustion air gets to the fire because the house is too tightly sealed
  • The flue is not warmed sufficiently

No matter which type of creosote is in your chimney, our professional chimney sweeps have the skill, knowledge, and tools to remove it for you.


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869 Main Street, Highland, WI 53543
(608) 929-4887
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(563) 582-5156

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