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What is Creosote? How Can I Reduce Creosote Buildup?

Monitoring Cresote BuildupIf you have a fireplace or wood burning appliance, you have most likely been told that you need to have your chimney annually cleaned by a certified chimney sweep to remove creosote buildup. Few people stop to explain what creosote is and why it is so important to get rid of. We don’t want to keep you in the dark. We have compiled the most important information that you need to know about creosote.

What is Creosote?

Creosote is the leading cause of chimney fires. It is a smelly corrosive material that is incredibly combustible. It is produced by combustion gases that are given off from burning wood. When the temperature in your flue is below 250 degrees Fahrenheit, these gases condense in your chimney and buildup along the lining of the flue. Since flue temperatures often dip below 250 degrees, creosote regularly builds up.

Extreme heat and burning embers that drift up through the chimney can ignite creosote buildup. If there is an extensive amount of creosote, the fire could spread to your home. It is because of the large number of chimney fires sparked by creosote that the National Fire Protection Association (NFPA), a nonprofit organization that has been committed to preventing fires since 1896, recommends annual chimney cleanings.

Stages of Creosote Buildup

Creosote BuildupCreosote takes different forms, or has different stages, as it builds up. Each subsequent stage is more hazardous and more challenging to remove.

Stage 1: In the first stage, creosote is soft and flaky like soot. Stage 1 creosote is easy to remove with a basic chimney brush.

Stage 2: Once creosote reaches the second stage it condenses into a hard, shiny flaky substance that clings to flue lining like tar. Though it may look flaky, Stage 2 creosote cannot be brushed away easily. The most effective way to remove stage 2 creosote is with a powerful drill that has metal rods called a rotary loop.

Stage 3: The goal of every chimney sweep is to stop creosote buildup from reaching this stage. Stage 3 creosote is a sticky, highly concentrated fuel. If you looked down a chimney with stage 3 creosote, it would look like tar was dripping down the inside. This tar-like substance hardens along the chimney lining and thickens as more creosote condenses. The thicker and harder it is the more combustible it becomes and the more challenging it is to remove. Chemical removers can be used in some cases to clean up stage 3 creosote. A rotary head with chains can also be effective when it has hardened and is not sticky, but this option is not recommended if you have a clay or ceramic chimney lining since the process can dislodge broken pieces of the lining. In many cases, the best option is to remove the flue lining and replace it.

Without proper equipment and training, it is smart to leave creosote removal to professionals.

Ways to Minimize Creosote Buildup

If you have a wood burning fireplace or stove, it is impossible to completely eliminate creosote buildup but there are ways that you can minimize it and prevent it from reaching stage 2 or 3 before your next cleaning. These are the best ways to reduce creosote accumulation:

Burn Seasoned Firewood in Discount Wood Burning Fireplaces1. Only burn seasoned firewood that has dried for 6 to 12 months. New wood contains a large amount of moisture. Wood with a higher moisture content produces more smoke when it burns. This smoke turns to creosote. The drier wood is the less smoke is created, the less creosote is produced. Buying a moisture meter from a hearth retail store or from a hardware store will help determine when certain wood is best for burning. Make sure to split a log in half before testing since the outside or bark of a log may be dry but the inside is still holding moisture. (Wet wood also decreases total heat output since an extreme amount of energy is wasted in your fireplace on boiling and evaporating the water inside each log.)

2. Insure your fire has sufficient air flow. Air is an important ingredient for an efficient fire. If your fireplace has glass doors, it is wise to open them so that your fire can breathe. This will allow your fire to burn hotter which burns a greater amount of the combustion gases. Most modern fireplaces, stoves, and inserts are considered “high efficiency”. Nearly 95% of the hearth products sold by UFS member stores are high efficiency, and are an excellent choice for homeowners that want the proper amount of air flow and a slow burning, hot fire.

3. Build hot fires that burn efficiently instead of slow-burning, smoldering fires. How you arrange firewood affects the fire that is created, pack it tightly—with modest gaps in between for airflow—so that it will burn cleaner. Make sure not to close the fireplace doors (ceramic glass) or restrict air flow adjustments too soon before the fire gets hot enough. A good indication that your fire may not be hot enough is if it starts to smolder and look like it might die out. At that point, the glass will also get dirty fairly fast and you are sending excess gases up the chimney. Keep in mind high-efficiency chimneys are smaller than traditional masonry flues or decorative fireplaces so creosote build-up is even more important. New high-efficiency fireplaces also have re-burning features such as secondary air tubes and catalytic combustors that require high-temperatures to operate functionally and cleanly. Keeping cool, smoldering, small fires with wet wood is the surest way to build creosote in high-efficiency fireplaces and clog bird/pest screens.

4. Avoid burning artificial logs. Artificial logs create a large amount of combustion gases that condense into creosote.

5. If you chimney is on the outside of your house, warm the flue before lighting a fire. Cool temperatures in the flue create more creosote. A good way to warm the flue is to make a torch out of rolled up newspaper and hold the lit torch under the open damper until you feel the air warm and feel the draft reserve.

Hopefully this information has helped you to understand why creosote removal is stressed so frequently.  We hope that you will stay safe and warm as you enjoy your fireplace this winter. If this post has reminded you that you need to schedule a chimney cleaning, please contact one of our certified chimney sweeps. We would love to work with you!

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