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What Is Creosote?

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While homeowners try to keep their chimneys and fireplaces clean and in good condition, many do not understand the importance behind having their chimneys professionally swept each year. The primary purpose of having a chimney sweep is the removal of creosote, a harmful buildup that is created by all fuel burning fires.

What is creosote?


Creosote is a sticky or tarry buildup in the chimney or fireplace that is created by all fuel burning fires. Creosote is most commonly associated with wood burning fireplaces and stoves, but can also be created in smaller amounts by heating appliances that burn coal, propane, or natural gas.

Creosote is more than just a sticky buildup, however. It is also extremely flammable; the more creosote that is present in your chimney, the greater your first for accidental chimney fire. Creosote ignition from stray embers or sparks from the fireplace is the primary cause of chimney fire.

In addition to increasing the risk of an accidental chimney fire, creosote buildup can also lead to a stinky chimney. Large amounts of creosote can create a distinct, unpleasant smoky smell that can permeate the whole house. Chimney odors caused by creosote are typically worse during the hot and humid months of summer, and can also be magnified by drafting problems.

Three stages of creosote

Despite starting as a thick liquid, creosote can be found in the chimney structure in many forms as it hardens over time. There are three stages of creosote.

  • Stage I: Stage I creosote is often described as a velvety soot. In this stage, creosote is very fine and is often mistaken as normal ash or soot buildup.
  • Stage II: Stage II creosote is the most commonly found stage of creosote. At this stage, creosote is seen as a crunchy, dry, and thin coating that can be easily brushed away by a chimney sweep.
  • Stage III: Stage III creosote is the most serious and hard to remove form of creosote. Also known as glazed creosote, stage III creosote is a dark, sticky, and thick and can harden to a glassy finish. Glazed creosote may not be able to be removed by brushes alone; in some cases, special solvents or even replacing portions of the flue are necessary.

How to prevent creosote

There are a number of ways that homeowners can prevent excess creosote buildup in their chimneys.

  • Buy and burn seasoned hardwood firewood. The moisture content in freshly cut wood can create excess creosote.
  • Do not allow stoves or fireplaces to smolder or burn at low temperatures. At a low temperature, enough hot air to completely blow the products of combustion up the chimney may not be present.
  • Make sure the flue is the correct size for the size of the fireplace or stove. An improperly sized flue can create drafting issues, allowing products of combustion to remain in the flue.

While small amounts of creosote are created by all fuel burning appliances, it is possible to manage and minimize the damage creosote can create. To find out more about how creosote can damage your chimney or to schedule a chimney sweep appointment, contact Guaranteed Chimney Service today!