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How To Prevent Creosote From Taking Over Your Chimney

How To Prevent Creosote From Taking Over Your Chimney

Creosote is a tar-like substance that forms within the flue of any appliance that burns solid fuel products, like wood or coal. It is formed when hot gases reach the top of the chimney and interact with cold outside air, creating condensation along the walls.

The gases that mix with the cold air are by-products of the fuel, so the condensation eventually solidifies and builds up along the walls of your vent piping. Wood is the absolute worst for creating creosote while burning coal isn't as damaging.

Why do I care if it's in my chimney?

How To Prevent Creosote From Taking Over Your Chimney
House Fire

You should care about creosote for two reasons:

1) It is expensive to clean up: If you ignore it and allow it to build up when it gets to stage 3 of the solidifying process, it is very expensive to remove. Special tools will have to be used and you will most likely need a professional to help you remove the tar without ruining your chimney.

2) It can cause a chimney fire: Of the two possibilities, option 1 is actually the least dramatic. So, that should tell you leaving creosote to build up for months on end isn't a good idea. Creosote is highly flammable and, if left untreated, will eventually cause a chimney fire and potentially destroy your house if it spreads outside the chimney.

Things that encourage buildup

Now that we know leaving creosote untreated isn't an option, let's discuss some of the main ways creosote can form and how you can help prevent that from happening.

1. Chimney offsets/elbows

How To Prevent Creosote From Taking Over Your Chimney
Chimney Elbow

A normal vent allows gases to escape straight up the chimney with minimal contact to the walls. When a chimney flue has a bend in the piping, it causes the gasses to slam into the walls on the way out. When the gas makes contact with the walls, it moves slower up the flue because it loses momentum. So, this leaves more time for it to attach to the walls and create issues for you.

2. Exposed Venting

How To Prevent Creosote From Taking Over Your Chimney
Exposed Chimney

As I mentioned earlier, creosote is formed when hot gases in your chimney mix with cold air outside. So, if you have a chimney that is heavily exposed to outdoor elements, you will have a harder time fighting creosote than other people. It is best to enclose your chimney within the building structure and allow five feet or less of the vent to extend outside of the building. Enclosing metal venting within an insulated chimney chase will go a long way in helping keep your flue warm so the condensation doesn't build up as quickly.

3. Poor Maintenance

How To Prevent Creosote From Taking Over Your Chimney
Worker looking inside a chimney

Chimney sweeping is key to maintain the health of your fireplace. Regularly sweeping your chimney doesn't give creosote any place to form. There is no way to prevent it from being created, but a good chimney sweep can definitely keep it from building up.

How often you use your fireplace or appliance will determine how often you need to sweep. Using it a few times a year doesn't necessitate sweeping every month. Every few months will be fine. Though, using the appliance as a main source of heat means you'll need to sweep about every month.

Also, doing a chimney check-up at the beginning of each burn season will go a long way in preventing issues. You can use a flashlight to see how built up the creosote is along the flue and go to war on that pesky tar!

4. Wrong type of fuel

How To Prevent Creosote From Taking Over Your Chimney
Pine Tree

What many people don't realize is not every type of wood is fireplace friendly. Sure, some woods are more readily available in your area. It might seem like a no-brainer to obtain whatever is closest or most readily available to you. Though, softwoods like pine, fir and cedar burn very hot. Because they burn so hot, they increase chimney temperatures rapidly, while also burning down quickly. The quick burn down creates a rapid shift from high to lower flue temperatures, aiding in the formation of creosote.

You should avoid using these in an indoor fireplace as much as possible unless they are used in small quantities as kindling wood.

5. Incorrect chimney sizing

How To Prevent Creosote From Taking Over Your Chimney
small chimney system

Due to increasing regulations on wood burning appliances, many of them operate very efficiently and release little pollution into the environment. This "environmentally friendly" approach can create a false sense of protection when it comes to chimney maintenance. Many flues are smaller than they used to be. So now, when people see an 8-inch vent pipe in their home, they assume an adapter can quickly connect to their highly efficient 6 inch stove pipe. This is not true.

If you don't connect your appliance to the proper size vent system, the stove won't perform properly and will cause gases to get backed up in the flue. As we learned earlier, the last thing you want is slow-moving gases in your vent pipes. The ideal ratio is 1 sq inch of flue to 10 sq inches of fireplace opening. This ratio will ensure the gases will have enough room to flow through your vents without stagnating.

How bad is my creosote buildup?

So, let's say you ignored everything we just said and decided you aren't worried about creosote anymore. You're throwing caution to the wind and not sweeping your chimney for the next year. What would happen? How do you know when you've gone too far and done irreversible damage?

Stage 1

How To Prevent Creosote From Taking Over Your Chimney
stage 1 creosote

If the soot buildup is a light gray dust that coats the walls, you're in stage one. This dust is smooth and covers your flue evenly. At this point, you can easily remove it yourself using the right chimney brush. If you have a metal chimney, you will need a poly brush because steel bristles will wear down the flue. Steel bristled chimney brushes are only necessary for masonry chimneys. They ensure all gunk is removed from mortar joints.

Stage 2

How To Prevent Creosote From Taking Over Your Chimney
stage 2 creosote

During stage two, a semi-glassy appearance takes over the dusty, flaky look of stage one. It can feel tacky or sticky. You may be able to peel off some of the creosote, but most of it will stick to the wall firmly. You can attach one of the above-mentioned chimney brushes to a fiberglass chimney rod to help ease the process of cleaning. These rods can reach up to 35 ft, so they are a gift if you want to stay as sootless as possible while cleaning. Running these tools up and down your chimney a couple of dozen times, or until the walls are mostly ash-free, will do the trick.

Stage 3

How To Prevent Creosote From Taking Over Your Chimney
stage 3 creosote

Well, if you made it this far, you have some splainin' to do. This is the point where the creosote looks like tar and sticks like glue. As an added bonus, when it gets super hot, it will re-liquefy and drip combustible balls of tar into your fireplace. It is very flammable at this point and can easily cause a chimney fire. The cleanup process is difficult because there are several layers of buildup that have to be broken through to remove it completely. RoVac ButtonLok Chimney Chain Whip and Adaptor will break it apart, but it is such an aggressive tool your fragile clay chimney tiles may fall apart underneath the force.

Cleaning Techniques

Top-down cleaning

How To Prevent Creosote From Taking Over Your Chimney
top down cleaning

Top-down cleaning means you clean the chimney by standing on your roof and push the chimney brush down the flue. This option is best for many chimneys because you can seal off the opening to the fireplace and prevent ash from coming into your home. Once the chimney is swept you can easily vacuum or sweep out the leftover soot.


Bottom-up cleaning is best for tall chimneys or ones containing elbows in the flue. Wohler Viper cleaning system utilizes a roll type cleaning rod and highly flexible spring action brushes that allow the system to be fed up through chimney dampers and stove flue openings. Even though most of the dust is prevented from moving around with this method, you should wear a respirator when cleaning.

Well, we've reached the end of the article. As always, you can call our NFI certified techs with questions or concerns. We hope you learned a lot today. Most importantly, treat your chimney right and it will burn well all season long.

About the Author

Collin Champagne

With over 13 years in the industry, Collin is a National Fireplace Institute (NFI) certified technician and managed content for the eFireplacestore and eCanopy brands. He has achieved the highest NFI certification possible as a Master Hearth Professional and is certified in all three hearth appliance fields: wood, gas, and pellet. With experience with sales and in-field installations, his expertise shines through his technical knowledge and way with words.

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Customer Q&A with Product Specialists

Chris C. from Muncie Indiana asked:
I can't figure out my woodstove. How do I prevent dripping creosote?
I can't figure out my woodstove. How do I prevent dripping creosote?
The first things would be to make sure that your wood is a dry, well seasoned wood, so the fire can burn hot and not deposit creosote. Typically a moisture meter can help make sure your wood is properly seasoned. Also, stove pipe should be running like down spout will all of the crimps pointing back into the flue collar on the stove. This allows creosote to funnel back into the unit, instead of out of the joints in your stove pipe.
Answered by: Cody S. on Dec 26, 2023


Alice from Cass County Michigan asked:
Is it helpful in keeping sone creosote off to tap on the metal stove pipe to loosen creosote and let it fall back into my little Lopi cabin wood stove?
Is it helpful in keeping sone creosote off to tap on the metal stove pipe to loosen creosote and let it fall back into my little Lopi cabin wood stove?
For safe operation of a wood stove and for creosote removal, a qualified chimney sweep should clean the system.
Answered by: Jason W.


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