If your home has a wood-burning fireplace, you may have heard the term creosote. What is creosote? It isn’t something you want to have in your chimney, that’s for sure. Creosote is a toxic substance created by burning wood. When wood burns, it releases more than just smoke—water vapor, wood particles, gases, minerals, and tar fog all go up the chimney. The chimney is typically cooler than the firebox where the wood is burning, and that change in temperature causes the smoke byproducts to adhere to the inside of the chimney. Creosote is the resulting substance.

Creosote is one of the leading causes of chimney fires, so don’t ignore your fireplace if it starts making strange noises or begins to smell funny when you start a fire. Fireplaces should be inspected every year by a qualified chimney sweep to ensure that creosote is not allowed to accumulate and that the chimney is safe to use. Your chimney sweep may mention the three stages of creosote, so read on to learn more about them.

Stage 1

Creosote in its first stage is not a good sign, but this is the best time to catch it and correct the problem. Stage 1 creosote is flaky and dusty, and it can be removed by a chimney sweep’s brush.

Stage 2

In its second stage, creosote takes on a consistency closer to tar and can become crunchy as it hardens. To an untrained eye, it may look flaky, but it has, in fact, already adhered strongly to the chimney liner. Removal of stage 2 creosote requires the use of a rotary loop tool attached to a drill.

Stage 3

Final-stage creosote is very dangerous and can sometimes indicate that a chimney fire has already occurred. Stage 3 creosote has a wax- or tar-like consistency that forms a hard glaze on the chimney liner when it cools. In this stage, creosote is at its most concentrated and flammable, and it essentially acts as fuel for a chimney fire. Although stage 3 creosote can be removed in some cases, the process can damage clay or ceramic chimney liners. For this reason, most chimney sweeps recommend that the chimney liner be completely replaced if stage 3 creosote is present.

Creosote Prevention

Creosote is indeed dangerous, but there’s no need to vow never to use your wood-burning fireplace again. In addition to annual inspections and cleanings, there are steps you can take to reduce the likelihood of creosote buildup. Burn only dry, well-seasoned wood. New, wet wood contains moisture that will evaporate and create a lot of smoke as it heats up and burns. If you have logs to burn, split them before building a fire with them to ensure that you’re not using wood that is dry on the outside but still wet on the inside. Build hot fires that have plenty of airflow so that the wood burns efficiently. Slow-burning, smoldering fires release combustible gases that contribute to creosote buildup, while a hot fire will burn up the majority of those gases. Finally, if your chimney is on the outside of your house, warm up the flue before starting a fire. The change in temperature between the firebox and the chimney is a factor in creosote buildup, so warming the flue with a torch made of rolled-up newspaper is a good way to minimize the temperature difference.

Creosote removal is not something you should attempt on your own. Cleaning a chimney is also a task best left to the professionals. Chimney sweeps have specialized equipment, knowledge, and training to get the job done correctly and safely. Keep in mind, too, that creosote can be difficult—if not impossible—to see from simply peering up the flue. It is also entirely possible for all three stages of creosote to be present in your chimney at one time. For these reasons—as well as for the health and safety of everyone in your home—yearly chimney inspections and cleanings are incredibly important.

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Sources: Ask the Chimney Sweep; Chimney Safety Institute of America; United Fireplace & Stove.

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