Creosote – What is it and where does it come from?

When it comes to owning a fireplace or wood stove, it’s essential to keep your chimney in good condition to ensure the safety of your home and family. One aspect of chimney maintenance that is critical to address is the buildup of creosote.

Let’s explore what creosote is, how it forms, and what steps you can take to keep your chimney free of this hazardous material.


What is creosote?

Creosote is essentially tar given off from burning wood. You may be wondering, where does creosote build up the most? Since we burn wood in our fireplaces we find the buildup of creosote on our chimneys. When you burn wood, the byproducts from combustion goes up your chimney as smoke. The substances are expelled out of the cooler chimney. Thus they condense and collect on the walls. The result is highly flammable creosote on the inside walls of your chimney or liner.


You may also be wondering, what does creosote look like? Well, that depends because there are three different types of creosote:


1st Degree Creosote

This is mostly ash soot so it is easily removed. A chimney professional’s brush is usually all that’s needed to get the job done. The thin layer comes off with little effort and is caught at the bottom with a specialized vacuum system. This is normal and should be cleaned once a year. These are the best chimney conditions. Below is how to properly use your fireplace. With this in mind, you can keep the conditions of your chimney and your home safe.

  • Good wood combustion
  • Relatively high temperatures in the chimney flue. This lowers the amount of condensation taking place.
  • Burning seasoned hardwoods. Hardwoods are dense, create better coal beds, and burn hot! Unseasoned and softwood, such as pine and fir, hold moisture and saps that increase the amount of creosote.
  • No doors on the fireplace. Make sure your logs have plenty of oxygen during combustion. Air creates higher burning temps. That warm air heats your chimney thus lowering condensation.


2nd Degree Creosote

This cleanup is not as easy. It cant be removed by a simple brushing but is usually possible. Instead of being a softer ash, the byproducts are in the form of shiny, black hardened wafers. Think of hard black shiny cornflakes. Restricted airflow causes your logs to burn at lower temps. A  Colder chimney equals more condensation because of less efficient burning.  Burning logs in fireplaces and wood stoves with glass doors typically results in this. This form of creosote is flammable. Try and keep those doors open and give your fire some airflow. Get your chimney inspected and cleaned as soon as possible. It is advisable not to burn a fire until doing so.


3rd Degree Creosote

3rd Degree Creosote is by far the most difficult to clean. In fact, there are times when the only way to make a chimney safe is to install a new chimney liner. This degree of creosote is a tremendously concentrated and combustible fuel! It looks like tar running down inside the flue. It can look like large, hard shiny bubbles. Every time its reheated it drips and collects like candle wax. As a result, the creosote gets hardened, then re-coated and hardened again. It becomes filled and dense. This is a highly dangerous situation with the potential for disaster! A chimney fire at the very minimum is very likely. Chimney fires are loud and hot. You can feel the vibrations like a jet engine stuck in your chimney. Do not use your fireplace. Have it inspected immediately!



How to Prevent Creosote Buildup

There are several steps you can take to prevent the formation of creosote:

  • Burn only seasoned wood: Make sure the wood you burn has been properly seasoned for at least six months. Seasoned wood burns more efficiently, produces less smoke, and reduces creosote buildup.
  • Maintain a hot fire: Burn wood at a high temperature to ensure complete combustion, which reduces the amount of creosote that forms.
  • Use a chimney cap: Installing a chimney cap can keep rain, snow, and debris from entering your chimney, which can reduce the amount of creosote that forms.
  • Regular chimney cleaning: It’s crucial to have your chimney cleaned at least once a year by a professional chimney sweep. Regular cleaning can remove creosote buildup and help prevent chimney fires.


Keep a watch for the following conditions. If avoided, you can ultimately keep your chimney safe and happy.

  • The air controls on wood stoves are significantly turned down.
  • A chimney has no insulation or is cold for some reason
  • Unseasoned and green firewood is being used.
  • The flue is too large for the appliance it is attached to.
  • A sufficient amount of combustion air for the fire cannot be drawn because the house is too airtight.

Creosote is a dangerous substance that can form in your chimney or stovepipe when wood is burned. It is essential to take precautions to prevent the buildup of creosote, including burning only. You can ALWAYS call 1800 Chimney to inspect your fireplace and chimney. Our technicians are certified and fully qualified.