How To Remove Creosote Buildup


What is Creosote?

Creosote is a flammable and corrosive substance that can build up on the walls of your fireplace and chimney. Creosote is formed when unburned wood particles, fly ash and other volatile gases combine as they exit the chimney. If there’s a poor draft, these unburned particles and gases can condense and build up on the walls of your chimney. Over time, these creosote or soot buildups can become a danger as they can potentially result in a chimney fire.

Causes of Chimney Creosote Problems

Smoke, or better termed, flue gas, is released by the initial fire, or primary combustion. Burning wood, no matter how it is done, releases pollutants in the form of gases and particulate matter. Flue gas, comprised of steam and vaporized but unburned carbon based byproducts (vaporized creosote). If smoke exiting the chimney is cooled to below 250 degrees Fahrenheit, the gases liquefy, combine, and solidify to form creosote. A flue too large for the woodburning appliance may increase the likelihood that creosote will build up. Restricted air supply, unseasoned or rain-logged wood, and cool surface flue temperatures also encourage creosote to build up.

Creosote Stages:

  1. Condensation: In an attempt to save fuel, many people reduce the amount of air entering the combustion chamber, causing the appliance to smolder. This has serious side effects. Smoke then cools as it rises in the chimney, not having enough heat energy to escape the stack. The flue gas then condenses on the inside of the chimney and the sap/resin turns into creosote.
  2. Liquidation: This sap/resin turns liquid and can seep into mortar joints or cracks in the flue tiles. The corrosive property held by creosote destroys masonry work and jeopardizes the life of your chimney.
  3. Solidification: As temperatures fall and rise within the chimney, causing the heating and cooling of the creosote. This quickly enables build-up, reducing the amount of space the flue gas has to exit the chimney and, in extreme cases, blocking the flue completely. This build up can look like tar and is frequently termed “tar build-up.”
  4. Friable State Creosote: When the solid creosote is burned, all volatile oils are removed leaving a residue that appears very similar to honeycomb which is crisp and easy to sweep from chimneys.

Creosote Glazing

Glaze is formed in the solidification stage and occurs when new layers of creosote are being added so quickly that the layers below it have no time to dry. These fresh layers then insulate previous deposits so it eventually solidifies creating the rock-like substance known as glaze.

How to Remove Creosote Glaze

acs-buynowacspowder-buynowTo remove this hard-as-a-rock glaze, it must first be broken down chemically. The two best products to use are Anti-Creo-Soot (ACS) Liquid spray or ACS Powder. ACS in liquid form is a chimney creosote removal spray that can be applied directly onto the fire or used to pre-treat the wood before burning. The vapor goes up the flue and attaches to the glazed creosote and chemically modifies it, converting it into a harmless ash that can easily be swept out with a chimney sweep brush. ACS in powder form is a little bit more powerful. This powdered chimney creosote remover is applied to the chimney walls and up the flue. When you start a fire, the temperature needs to reach 300 degrees F. Once this happens, the ACS Powder causes the creosote to expand and contract at a different rate than the flue it’s attached to, causing it to peel away from the flue liner. Both of these products contain unique chemical catalysts that breaks down the creosote over time. They are the most powerful when used in combination. Use the ACS Powder for the first 2 weeks to break down the really heavy duty creosote. Then use the regular ACS liquid spray every time you have a fire. Give it 5-6 sprays each fire to reduce creosote buildup and keep your chimney creosote-free.

After you solve your creosote problem, it’s a good idea to check the rest of your chimney and make sure it’s in good shape. Keeping your bricks waterproofed and performing chimney crown repair if needed are essential steps to take to keep your chimney in proper repair.


43 comments on “How To Remove Creosote Buildup

  1. Jimmy Moore on said:

    I have a problem with creosote buildup in my wood-burning furnace. I have shared my problem with the manufacturer and they told me to contact your company for help. The creosote is inside the heat exchangers. What do you recommend?

    Jimmy Moore
    Lawrenceburg TN

  2. chimneyadmin on said:


    Hire a professional to come out and take a look at the apparatus. There should not be any creosote building up inside the heat exchangers; the only logical place for creosote buildup is up in the flue system itself. This problem needs to be addressed by a professional.


  4. We have a problem. We just moved into a house & it appears that the chimney is completely blocked with creosote. It looks like the previous tenants tried to use a chimney brush from the top causing the “honeycomb” creosote to fall and blocking the entire chimney about 6′ up from cleanout box. My husband has tried pounding a steel rod through to punch a hole in the dense creosote but nothing seems to be working. Do we have any options? Are there any chemicals that can work to dissolve the creosote without being burned? Obviously we can’t burn/use the woodstove until the smoke has somewhere to go. Any practical advice you can offer is greatly appreciated.

  5. askthechimneysweep on said:

    The tiles will probably have to be removed from this chimney flue system and an insulated stainless steel liner installed. If you are considering burning wood in this fireplace, it would be prudent to have the chimney properly lined. This is a radical situation that we don’t often see, and due to the severity of your buildup, my professional opinion is to have a professional come out to estimate the creosote and tile removal and installation of a chimney liner. Refer to professionals that are licensed by the National Chimney Sweep’s Guild, which you can check out on their webpage or the Chimney Safety Institute of America Hope this helps! Burn safe and warm.

  6. Uncle Ben on said:

    I have a 15 year old fireplace and chimney. I burn maybe 15-20 fires a year using seasoned wood. The damper is always wide open and I don’t
    have any of the symptoms of a clogged flu. Never been cleaned. Am I
    on thin ice?

  7. about 10 years ago, I had a chimney fire in the flue of my wood burning fireplace insert. I was lucky in so far as I did have a couple of sticks of “Chimfex” to throw into the insert after I heard the roar and saw flames shooting out of the chimney stack (which lit up the cold winter night). Chimfex chokes out fire when thrown into an air-tite stove. My local fire department came quickly to crawl onto the roof and into the attic to determine that nothing had caught fire in the house structure, although the aluminum cap over the flue did melt in the fire-blast. I then contacted a professional to look at my setup, which I had gotten when I purchased the home a few years earlier. The metal flue from the fireplace insert only went about 4 feet up the chimney, then ended leaving the smoke and creosote to buildup on the interior of the chimney masonry… which it did for at least 4 years while I had lived there. He cleaned everything, then installed a double wall stainless liner, which he wrapped in a mineral wool blanket ( to help keep flue temps up and creosote buildup down) down the entire length of the masonry chimney. He also fabricated a connector from the round flue to the rectangle opening at the back of the insert. He capped the flue with a SS flue cap to keep out birds and such. The cost was nearly $2,000 10 years ago, but the thought of another chimney fire made me spend the money for peace of mind. Here I am 10 years later… I typically burn a really hot fire every 3 or 4 burns for at least an hour, ( I burn almost every day in the winter) and throw in one of those anti-creosote sticks that look like a flare into the fire every couple of weeks. Last November I had my chimney swept for only the second time in 10 years, and although it needed it, the buildup flaked off easily. In your situation, I highly recommend getting a good pro to look at your particular chimney and then spend the money to get it fixed correctly. A chimney fire is no fun at the least and life-changing at the most. I go to bed every night in the winter warm and content in the knowledge that I have done everything to keep my home from burning down that I can.

  8. askthechimneysweep on said:

    Great report on the Chimfex I hope every wood burner hears you loud and clear. I like the statement regarding the professional inspections and service work! It sounds to me like your getting away without a lot of sweeping. I would keep checking the flue pipe regularly and keep changing those batteries in the smoke detector and carbon monoxide detectors. That is what will wake you up at night if their is a problem.
    Sounds like you’re burning safe and warm

  9. askthechimneysweep on said:

    You bet you are! National codes state inspection should be done yearly . 15 x 15 is 300 fires, and whether these are one night fires or three day fires plays a factor in the equation as well. My point is that I would at least inspect the chimney system once a year at a minimum or after each cord of wood burned. Get your ice skates on, or I would recommend getting off the ice.
    Burn Safe and warm!

  10. alan on said:

    a chimney sweep service said i need to have my flue cleaned over two sessions by what they called a PSR Treatment. could you please explain this treatment / process

  11. chimneyadmin on said:

    I am not sure what that is? I would ask to see the manufacture information, I am sure that they will have a website you can look at. Read the contract before you sign. They should also give you a referral and if any a 800 number.

  12. fenton thompson on said:

    I have a wood add on my furnace my problem is creosote ran down my outside of my chimmey all over my vinyl siding how do you remove this

  13. chimneyadmin on said:

    I feel that you are treating the symptoms and not the problem here. You first need to resolve the creosote problem and why there is a continuous buildup. Without seeing it I would guess it’s one of three things.

    1) The cap is being clogged because the fire is being chocked down to much.

    2) Second, it’s improperly sized off the back of the furnace. Code standards state that the venting size needs to be the same sq. inches off the back of the furnace unit all the way through the entire chimney. In other words you can’t mix sizes of pipe or chimney flue venting sizes.

    3) Three your fire wood is unseasoned and is causing an excessive creosote issue.

    After the creosote problem is resolved, I would go to a local hardware store or big box store and ask for a product that might work without damaging the vinyl siding. I would test small areas before you clean the whole vinyl wall, to make sure it will not damage it.

  14. Bob Bennett on said:

    We had our chimney (fire place) swept the other day and at the end the fellow told us about other repairs that he would recommend doing. Some immediately (see below) and others in the coming 1-3 years (fixing the cap). One recommendation is to have our chimney chain whipped due to cresote buildup at the bottom of the flue. He said the top of flue was fine.

    Last thing I want is a chimney fire, but from what I am reading about creosote (this site and others), most comments discuss using a catalyst to help break down the creosote and few mention chain whipping as a first option. I do have experience with fire places/wood stoves and understand the importance of buring hot fires and recognize that this past winter I did have some moist wood and the fires weren’t as hot as usual.

    Additionally, there was something about the sweeper that made me feel like he was trying to up-sell me on other services (e.g. he can clean my dryer vent hose for $150!). I will obviously start using anti-cresosote sticks, but I would like to hear others’ thoughts on chain whipping.

    Thanks, Bob

  15. chimneyadmin on said:

    I also offer chain cleaning that is often referred to as Ro-clean or mechanical cleaning. This is process is completed with sections of chain or heavy braided steel wire attached to a specially designed spinning head. This head is connected to rods that are extended down into the chimney flue or up from the bottom. A heavy duty drill spins the rods and chain head at at a very rapid speed. This process then scratches the shinny glazed creosote off of the walls of the flue tile. More often then not, we are successfully able to removed about 90% of this shinny creosote and return the tiles back to their original orange color. be careful not to choke the stove down to much, burn very season wood and be sure the chimney cap screen is kept free of any creosote buildup.

    The dryer vent cleaning is another service that we and many other professional chimney sweep companies offer. Their are specific procedures to follow such as no screws or plastic vent piping should be used in the venting system. The accumulative length of the dryer vent run should be calculated and evaluated with proper metering and recorded before and after the dryer vent cleaning. $150 does not seam out of line for a professional who knows what they are doing, insured properly and softer brushes and more flexible rods that are specifically designed for dryer vent cleaning. Here is little side bar, their are a lot more dryer vent fires then there are chimney fires and cause a whole lot more insurance fire related damage.
    Burn Safe and warm and stay dry ;-)

  16. I have a Queen Air Fireplace insert rated at 115,000 btu which was installed new in 1988. I am the second owner of the home, I have been using the fireplace to heat the home during the winter months here in Michigan. My flue is 12 x 12 clay I installed a cap on it 4yrs ago only because I was seeing water on the inside and rust had formed, but since then I have had a lot more creosote build up near the top of the chimney, I burn dry seasoned Ash wood only, have it cleaned twice during the six months of use and I burn on the average of 7-8 cords. My question is can the cap/screen be restricting or dampering down to much for this unit? is it possible that it was made to burn with a open flue? also seeing that I have some now creosote build up any thing I can spray or brush on to help break down over fall here before season starts back up? Thanks Dave

  17. Michael on said:

    I recently installed (3 weeks ago) a flexible stainless steel liner insert for a wood stove that have start using for the first time this year. Recently whenever I turn the dumpers down and head to bed or leave the house (so the fire won’t go out), I have been having problems with Creosote coming out of between the joins in the stove pipe above the wood stove. When I first noticed it I killed the fire, took apart the stove pipe, cleaned it and the applied a joint adhesive/sealer for stove pipe. The Creosote has seemed to have made its way through the sealer and is now coming back through the joints, again. This is all within 2 days! What should be done? I some need advise/solutions to help fix this problem, please.

  18. chimneyadmin on said:

    Take a moment and look at our videos of wood stove installation, firewood and also on creosote on our website
    I would request the service company in writing, to return and explain the problem and how it will be resolved. In thirty year of business I personally have never had to use sealer on any pipe joints. I personally believe smoke will always take the path of least resistance and will rise up in almost all properly sized venting systems. Remember, I stated properly size venting system. This means not down sizing the chimney flue system.
    Most building codes state that any solid flue burning appliance, the flue pipe size must be the same as the exit on the wood burning appliance.
    The screen on the chimney cap needs to be kept clean or totally removed.
    You cannot choke down a stove and not expect glazed creosote problem.
    Your firewood needs to be seasoned. This a very serious issue and must be resolved. I hope this shed some light on your creosote problem.
    Burn safe and warm

  19. We are having an issue with creosote weeping through the masonary work of our chimney. We have an 8 inch block chimney with a liner. We are using a 6 inch flue out of the stove. How do we stop the weeping?

  20. herbert heym on said:

    Do you have a solution to the creosote buildup on the ceramic glass door of my fireplace insert? Seasoned wood and high temperature are necessary but some deposit is still going to happen. Are there any recommended ways to clean off the window. I have used soft scrub for stove tops with pot scrubers with some success. Are there any other solvents that will work? Thank You.

  21. TomLaw2 on said:

    I have a new wood burning stove insert complete with a new flue system. The stove has a catalytic combustor. Are these chimney sweeping chemical logs/sprays safe for the catalytic combustor?

    Thanks in advance for the advise.

  22. chimneyadmin on said:

    It sounds to me like you do a lot of burning. I would recommend calling in a professional chimney sweep. It sounds like you may have an issue with improper lining. I cannot be sure because I have not inspected your fireplace. So again, I would call in a Chimney Sweep.

    Burn Safe and Warm,

  23. chimneyadmin on said:

    I know this doesn’t seem like much help but, I would check the manufactures recommendations. Look through your manual or even look for a contact number or website. Do this before using any chemical cleaners.

    Burn Safe and Warm

  24. Earl Russell on said:

    Hello I have enjoyed reading through the responses. I have a wood fired gasification hydronic boiler. From time to time I have experiencied creosote build up. This past year has proven a real challenge. My flues from the secondary burn chamber are clean. My sedondary flue chambers are mostly plugged. I have been using the chemicals to try to open them up so I can get my cleaning tools through. My inside dia is between 1.1/2″ to 1.3/4″ I have a rotary type of push scraper that does a nice job on the dry cresote. My build up is the sticky tar, tools and brush won’t go through the flues. What do you recommend?

  25. KarenB on said:

    I just had my chimney cleaned by the same company that has been doing it for years. They hit me with the need to have “stage 3″ creosote removed and have mortar repairs done – at an estimate of $4700. They are proposing treating a 20′ 13×13 area of the chimney with Creaway, then rotary mechanically sweeping it to get rid of the remaining creosote, then resurface the liner with Heatshield Cerfractory Flue Sealant. I asked why they had not seen this stage 3 creosote last year and they said it could occur with one fire. I called another company to inquire about an estimate, and was told that stage 3 creosote does NOT build up with one fire -this guy also told me that you can never get all of the creosote out, so he’d recommend tearing out and relining the chimney. I’m going to get another estimate or two but found your site and would like your opinion! Also, we questioned why this stage 3 creosote was not picked up last year, as we have our chimney inspected and cleaned every year. Thoughts?

  26. @KarenB – In most case that I aware of, 3rd degree glazing comes from using wet wood, or choking the damper down. I would think the first guy has the right approach…that is if there is damage to the interior of the chimney that can be verified with an interior camera system! HeatShield is a great product to repair a damaged chimney, but not to stop glazing issues. Check out our HeatShield and creosote videos.
    Burn safe and warm.

  27. I wrote in 2 yrs ago, concerned about the black tar running on my shingles from my chimney, I have a ROHN stove with a blower built in. I have fought 2 yrs finally coming up with, its the blower COOLING the wood stove off, to the point of CREOSOTE problems bad, I have unplugged the blower and my chimney is back to working order. I went as far as re splitting my whole woodpile, smaller pieces that is, I have called every sweep I could , and finally as a very last resort unplugged blower. seems like some one would of said SOMETHING about the blower especially as many folks I had contacted. I JUST had to share this. HAPPINESS is a clean burning woodstove after a cold day at work. Thanks Jack

  28. @ Herbert, I remove heavy buildup on the glass with a glass scraper, using a new blade to avoid damaging the glass. Of course a good hot fire will burn it off, but not entirely. I try to maintain this the days after with a vinegar-soaked soft cloth which easily removes a thin coating. Hope this helps

  29. Charity Gobeil on said:

    I have a wood boiler that has built up creasote on door and walls of it repeatedly. I have tried using the cresote burning products such has CLS logs and kwik shot with no effects. This build up on door of burner is very tar like and sticky. How can I remove this substance? Best way to prevent it? The boiler does have a blower, I leave the damper open during burning. I had the furnace guy that has serviced the oil and wood boiler for 10 years check it and hed adjusted it to set for 180 degrees to trigger the oil boiler off when wood is being burned and told me not to exceed 220 degrees max during burning or it will cause the water tank to dump. What is the best corse of action to burn safetly and keep boiler cleaned of cresote?

  30. chimneyadmin on said:

    Because you have an existing glaze creosote problem, I would first recommend contacting the furnace manufacture for their insights regarding installation. I would question the venting sizing of the chimney, as it must be the same size in Sq inches as the outlet on the back of the furnace.
    I would recommend seasonally removing the chimney cap/screening during the burning season! Remember to only burn , well seasoned firewood that has been cut, split and covered is for about 6 months
    Burn Safe and warm
    Clay Lamb

  31. Lisa B. on said:

    Rain came down the chimney and creosote “tea” stained the rocks and mortar under the chimney clean out.

    We haven’t had much success cleaning the porous surfaces. Many well meaning suggestions from people who haven’t actually tried them. Have you had success cleaning this? What have you used?

    We do clean our chimney regularly.

  32. chimneyadmin on said:

    This is a difficult situation to cleanup. But I think you have a bigger problem as Creosote tea that you referred to is and unusual occurrence. My insight would tell me that the draft in very sluggish in that chimney. Burn hotter fires, dryer wood, leave the damper wide open more often. The Cap on the chimney top should be preventing the snow and rain from coming in, while the screen on the cap must stay cleaned off at all times. I’m hearing some good thing from a company called American Building Restoration. They have some very interesting products that may remove this stain?…….Let us all know if this works
    Burn save and warm

  33. Edward on said:

    Chimney fires are potentially devastating. If you burn regularly, as I do in a fairly cold climate (Ohio), you should sweep at least yearly.

    I do think with the downturn in residential building since 2007, there are a lot of unemployed masons or underemployed masons branching out into chimney work.
    I had a guy who showed up, saw an admittedly quite dirty chimney, and immediately started talking about replacing the cap for $440 (really? at that price it should be copper with a decorative weather vane). He wanted $450 for the cleaning. But he did not have the equipment, after he showed up two full hours late. WTH? As I understand it, you use a chimney chain whip if you have something the brushes and rods won’t remove. What kind of outfit doesn’t bring that tool with them? Then he wanted to talk about putting a liner in, etc. Every word that came out of this guy’s mouth had a cha-ching cash register sound to it. Then when I talked about re-scheduling, the price had magically gone up to $500. I cut him loose, brushed it myself, hit some areas with a drill attachment, and ran a 750 lumen light down the flue. I still have not burned again, and I am thinking about hitting it with some chain flails.

    So is cleaning not recommended? No, if you burn a lot, you gotta clean or risk a devastating fire. If the creosote got glazed on from neglect, that’s very dangerous to leave in place and more time consuing to clean. But some chimney sweeps, especially those who double as masons give the business a bad name. Call around. Get some estimates. Use Angie’s list.

    Couple questions though: (1) when cleaning, do you really expect to get down to the original coloration of the flue tile? I.E., where my hot water and gas hvac vent, those flue tiles are remarkably clean. Does a good chimney cleaning really get the flue tiles back to that same terra cotta color? Or realistically, wouldn’t you have some permanent smoke discoloration?
    (2) Do the chimney chains run a risk of cracking the flue tiles?

  34. Edward on said:


    The 450-500 for cleaning glazed creosote, if that’s really what I have, may be in line.

    What I did not like was the constant up-selling. Assuming I needed a new cap. Assuming I may need a new stainless steel liner. I say show me some cracked tiles. Show me some failing mortar. In the meantime, winter is about done, and I just won’t burn until I get resolution.

    I see a lot of the steel liners are flex pipe. Drawing an analogy from car exhaust, you should never, ever use flex pipe on an exhaust manifold or piping for a car if you can avoid it. Show me any performance oriented exhaust header or pipes for a car that has ribs like flex pipe does, and I’ll tell you that’s less efficient and probably all show and no go. Why is it different for chimney flues? Isn’t that another sort of exhaust pipe? The original tile liners did not have ribs/ridges. Why would you put something in that’s going to collect soot and creosote in the ridges? Am I missing something here?

  35. on said:

    I have an open fireplace. I’ve cleaned out the firebox of all the friable soot and used a wire brush to remove the glaze all the way to the beginning of the flue. My question is; where do most chimney fires start? Up in the flue or in the firebox. . Finally, once the flue is cleaned of friable soot is it appropriate to use the ACS product?. Has anyone had real life experience with the ACS product and how well does it work. I had an online seller of ACS tell me it won’t work on glaze and I need a stage 3 removal product.

  36. akis tzortzis on said:

    I have a open fireplace measuring 1m wide by 40cm depth and 70cm height approximately. It has glass doors that you can close or leave open. It has two vents on either side that somehow radiate or heat air inside the room, but not the air/smoke of the fire. It also has an air brick on the outisde so it can draw cold air from underneath the fire, under the cast iron plates.

    I can run the fire with the doors open or closed. I had thought that with the doors open it would steal my air from the room and send it up the chimney resulting in a net loss of heat. However I ran it today with the doors open and it really pushes a lot of heat in the room.

    Is this simply my impression or it is better to keep the doors open?

  37. Originally Posted By Lisa B.Rain came down the chimney and creosote “tea” stained the rocks and mortar under the chimney clean out.

    We haven’t had much success cleaning the porous surfaces. Many well meaning suggestions from people who haven’t actually tried them. Have you had success cleaning this? What have you used?

    We do clean our chimney regularly.

    try TSP can be purchased at most GOOD hardware stores it is a powerful cleaner .. also can be used to wash roof shingles that have that same type of build up == do a test patch first as it tends to lighten many products

  38. Renee Harris on said:

    We use a fireplace for hear full time in the winter. The problem we have run in to is that on either side of the chimney, we have very large windows. At some point creosote last year creosote tar got on these windows. These windows get full afternoon soon all day so it has become baked on. We have tried lots of chemicals and even used a razor to scrape it off, with no luck. Do you have any other suggestions for us to try?

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