How Often Should I Clean My Chimney?
Chimneys for older stoves must be cleaned frequently
Most people know that chimneys need to be cleaned, but very few people think about it until a problem such as insufficient ventilation occurs. However, such problems can be considerably more severe than they initially seem – reduced ventilation can be the result of creosote buildup, which is a very flammable substance. Creosote is formed as a result of cresols and phenol compounds, chemicals which are released when wood is burned. It condenses on chimney walls when the chimney or flue is cooler than around 400 degrees Fahrenheit, and when there is high moisture content in the exhaust gases from the fire.
As you probably know, chimney fires can be relatively harmless if there is very little creosote build-up. However, if there is significant creosote residue in the chimney, it is difficult to put out a chimney fire – it must simply 'burn out', which can crack or damage the chimney liner in the best case scenario, and can lead to a house fire in the worst-case scenario. For these reasons, as well as the long life and effective operation of your woodstove or fireplace, it is vitally important that you have your chimney cleaned at regular intervals. Most manufacturers recommend having your chimney inspected monthly during the heating season if you are a heavy wood burner, which is to say that wood heat is your main fuel for home heating, while chimney cleaning is suggested yearly, or more often if problems such as creosote build-up are detected.
As long as the chimney temperatures stay hot, or at least frequently exceed 400 degrees Fahrenheit, creosote formation should be minimized. So because of this, not only unseasoned wood helps with creosote formation – smoldering fires or small fires lit "to take the chill out of the air" also greatly contribute to the fast formation of creosote in your chimney. Thus, a good hot fire does a partial job of cleaning your chimney, although it is in no way a substitute for cleaning by a licensed professional chimney sweep.
So the simplest answer is that your chimney should be cleaned often. Check with your local fireplace construction specs to see if there is a minimum cleaning interval in your area but failing that, plan to have your chimney cleaned at least once annually.