What is creosote?

What is creosote?

Creosote is a chemical product that is sometimes used as a wood preservative due to its preserving properties. However, it is also a residue that we encounter when we light our fireplace, as the combustion of wood produces this substance, which adheres to the walls and must be handled with care due to its high toxicity.

Creosote can enter the body through the skin, lungs, or mouth if proper measures are not taken to clean the chimney. The health effects can be very serious, as prolonged exposure is associated with certain types of cancer. That is why the European Union does not allow the use of creosote as a wood preservative.

How creosote forms in a chimney

When wood is burned, various types of acids are generated. These acids combine with the moisture released by the logs and heat, forming the waste known as creosote, which adheres to the walls and doors in chimneys. If too much accumulates, especially in the flue, combustion becomes more difficult and the chimney does not function properly. Therefore, it is necessary to keep the interior of the chimney as clean as possible if we want it to perform at its best.

How to reduce creosote buildup in a chimney

We cannot prevent our chimney from generating residues when we use it. However, it is possible to reduce the amount of creosote. To prevent excessive creosote buildup, simply open the damper of the chimney to the maximum when lighting it and keep it open for a few minutes. The wood will burn slightly faster, but the vapors will burn off sooner, reducing the moisture content.

How to clean the glass door of the fireplace

It is also important to use well-dried firewood. When the logs have not been properly treated, there may be moisture inside them, which increases the chances of creosote forming in the chimney.

Installing a door is a way to better isolate the chimney, reducing the humidity inside the fire and ensuring that the residues remain only there. The chimney draft is maintained at a higher temperature, which is also beneficial since the creosote does not harden and does not adhere to the walls, resulting in a smaller amount of soot accumulated.

Some chemicals facilitate the removal of creosote if there isn’t too much of it. For example, chimney sweeping powder, which is applied when the chimney is still hot, generates vapor that dries and removes the residues, causing them to fall into the base or tray to be removed.


Need to clean the chimney

As mentioned before, creosote is highly harmful to health. That’s why it’s important to pay attention to how to clean a chimney to avoid getting poisoned. Protective elements such as gloves and a mask should be used to prevent any dirt from entering through the skin or respiratory tract. It is preferable for the mask to be disposable, and for both the gloves and the clothing used to be washed separately from other garments to avoid transfer.

How to clean a fireplace

Types of creosote

There are three forms of creosote, and both can be harmful to human health and the environment if not handled properly, as they contain toxic and potentially carcinogenic compounds.

Vegetable creosote

It is a thick, oily liquid with a dark yellow or brown color obtained from the distillation of wood, especially wood from trees such as beech and pine.

Vegetable creosote contains numerous chemical compounds, such as phenols and cresols, and is mainly used as an antiseptic, expectorant, and disinfectant in traditional medicine. It is also used for wood protection against fungi and insects.

Coal tar creosote

It is a byproduct derived from the distillation of coal tar, a viscous and dark liquid obtained from the carbonization of coal. Coal tar creosote also contains compounds such as phenols and cresols, but in different proportions than vegetable creosote.

This substance is commonly used as a preservative and wood protector in construction, especially in railway sleepers and utility poles, due to its fungicidal, insecticidal, and water-repellent properties.

Creosote as wood combustion

In this case, it is a byproduct of incomplete wood combustion. When wood is burned in a fireplace, gases and particles are released which, upon cooling, condense on the inner walls of the chimney, forming a buildup of creosote.

This accumulation of creosote in chimneys can be dangerous as it is flammable and can cause chimney fires if proper cleaning and maintenance are not performed. Creosote can also block the chimney, reducing combustion efficiency and causing the release of smoke and toxic gases into the house.

How to clean a fireplace

Therefore, it is important to regularly clean and maintain wood-burning chimneys to minimize creosote buildup and reduce the risk of fires and associated health problems.

Differences between creosote and soot

Creosote and soot are two different byproducts generated from the combustion of organic materials such as wood, coal, or oil. Although both can accumulate in chimneys and heating systems, they have distinct properties and compositions.


As mentioned earlier, creosote is a byproduct of incomplete combustion of wood and is formed when the released gases and particles condense on the inner walls of the chimney. Creosote is a sticky, thick, and oily substance, with a dark brown or black color.

It contains a complex mixture of organic compounds, such as phenols, cresols, and tars. Creosote is flammable and can cause chimney fires if it accumulates excessively.

In addition, it is toxic and can be harmful to health and the environment if not handled properly.


Soot is a solid byproduct of incomplete combustion of materials containing carbon, such as wood, coal, or oil. It consists mainly of fine particles of black carbon, along with small amounts of organic and inorganic compounds.

It accumulates as black powder or flakes on the inner walls of chimneys, exhaust ducts, and heating systems. Although soot is not as flammable as creosote, it can cause problems in ventilation systems, reducing their efficiency and causing the release of smoke and toxic gases inside the house. Moreover, inhaling soot particles can be harmful to health, especially for the lungs and respiratory system.