What Is Creosote?

20 July 2016
 Categories: Construction & Contractors, Blog


If you own a home with a fireplace and chimney, you may have heard the word "creosote" used by chimney repair professionals, such as Excel Chimney & Fireplace Service. Knowing what creosote is and how it can affect your chimney is an important part of taking care of your home and preventing fires. The following frequently asked questions will tell you what you need to know about creosote.

What is creosote?

Creosote is a black or brown residue that builds up on the inside of a chimney when unseasoned wood is burned inside the fireplace. Creosote can be sticky and tar-like, flaky, drippy or shiny and hard.

Why is creosote a problem?

Creosote is highly flammable, and therefore can be a major cause of chimney fires. Chimney fires can do extensive damage to the house, often leading to thousands of dollars in home and chimney repairs. In addition, creosote is also smelly, and can cause an odor in the room where the fireplace is located.

How can you tell if you have creosote?

If you notice an odor in the fireplace, this is a warning sign that you have creosote. However, the best way to tell if your chimney has creosote is to call in a fireplace repair professional. He or she can inspect the inside of your chimney, measure the depth of the creosote, and make recommendations for cleaning.

How can you prevent creosote from building up again in the future?

The best way to prevent creosote from building up in your chimney is to burn firewood that has been fully dried (called "seasoned"). Seasoned firewood has low moisture content and can be safely burned in fireplaces. Unseasoned firewood, also called "green" firewood, causes flue gas to condense on the inside of the flue, thus leading to creosote buildup.

You can also prevent creosote from building up inside your chimney by having it inspected by a professional at least once per year.

How can you tell which firewood is seasoned?

Seasoned firewood will have many or all of the following qualities:

  • Dark yellow or gray in color.
  • Cracked ends.
  • Sounds hollow when two pieces of wood are hit together.
  • Lighter weight than green wood of a comparable type and size.

Seasoned firewood will burn comparatively easily, and will not produce any hissing noises or moisture while the fire is burning.

If you believe that your chimney may have a buildup of creosote inside the flue, contact your chimney repair specialist. He or she can help you determine if your chimney is safe to use.


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