Excessive Creosote Build-up

Q: My chimney was built in October 2014. I'm noticing that when there is a fire, the creosote drips out the clean out door. This is a big, messy problem. The chimney consists of 16” flue blocks with a 6” clay liner. The flue goes all the way to the ground and is about 8 to 10 ft above where the stove goes into it. All my wood was cut last winter and split and covered this summer past.

A: Excessive creosote* build up is usually caused by the burning of unseasoned and/or softer/sappier woods. It can also be caused by a weak draft** that allows smoke to spend too much time in the flue, thus cooling and depositing carbon rich chemicals onto the interior walls before exiting.


While your wood is seasoned, it may be a softer/sappier wood like pine and spruce. These will worsen creosote build up when burned.

Excluding the wood as the possible cause, this can be the result of a few things. One of the main reasons creosote builds up in a chimney is “smoke time residency”. The longer the smoke spends in the flue, the greater the chances for chemical compounds in the smoke to collect and harden on the sides of the flue. Especially if the chimney is on an exterior wall of the home, the flue may be too cold, allowing a lot of creosote to build up and drip down the flue and eventually onto the exterior or interior wall.
Another possibility is the exhaust on the stove could be too large for the volume of smoke and air that the flue can handle, allowing creosote to build up, however this is usually coupled with smoke spilling into the home.

It may also be that your clean-out door is not sealing well, allowing too much air to enter the flue, slowing down the draw, thus giving creosote more time to collect on walls of the flue. 

The Fix:

It basically boils down to improving the draft. Assuming you are burning seasoned hard woods like oak, cherry or maple; you have two things to try first. Prime (or heat up) the flue prior to operating your fireplace or stove and try burning hotter fires. Both of these will produce a better draft, resulting in less creosote build up. 

CSL or Chimney Sweeping Log

CSL or Chimney Sweeping Log

Another way to lessen and get rid of creosote is to burn anti-creosote logs occasionally throughout the burning season and have your chimney swept at the end of the season. You could also try adjusting or replacing the clean-out door so that it seals better. 

If these simple solutions do not work, you may need to invest in an insulated liner to to keep those flue gases warm and headed in the right direction.


That much creosote build up can be especially unsafe. You will need a CSIA Certified Sweep to remove the existing creosote and hopefully these simple solutions will solve the problem. Otherwise, the Chimney Sweep should be able to recommend a fix during their inspection.

* Creosote: A type of carbon rich chemical released during the burning of wood and other fossil fuels when there is a lack of adequate airflow. As the smoke rises through the chimney it cools, causing water, carbon, and volatiles to condense on the interior surfaces of the flue. This appears on the flue as a hard, dark, and shiny coating.
** Draft is the force or pressure difference between the inside and outside of the venting system which makes gases created by the unit draw up and out of the chimney.