The chimney walls in a fireplace used to burn wood accumulate soot and debris that needs to be cleaned away. Tar and creosote buildup inside the chimney are flammable, causing a potential fire hazard over time. Chimney-cleaning logs claim to give you an alternative to cleaning the inside of the fireplace and chimney by hand -- which is both messy and laborious -- by reducing creosote. While these logs reduce and loosen some of the creosote buildup, they do not clean the chimney as thoroughly as a professional chimney sweep can.
Chimney-Cleaning Log Claims
A chimney-cleaning log works when you burn it in the fireplace, much like a regular log. Burning a regular wood fire before adding the log softens tar buildup inside the chimney, which makes the chimney-cleaning log more effective. As it burns, the cleaning log releases chemicals that adhere to the chimney walls, loosening tar and creosote buildup or rendering it less likely to cause a fire. Some of that loosened debris may fall into the fireplace.
Which Logs to Use
Some logs do what they claim to do, but others may not. The Chimney Sweeping Institute of America rates these products to help consumers decide which are safe. CSIA-rated products bear a "CSIA Accepted Product" logo, ensuring safety. These also bear safety wording, stating that the chimney-cleaning log is not a substitute for an annual inspection and cleaning of the fireplace and chimney.
Falling Debris Dilemma
Debris that falls from the chimney walls after you use a chimney-cleaning log may end up in the fire, or more likely, it may land on the smoke shelf, a curved area or another obstruction within the chimney, which is most likely not a straight, smooth vertical shaft. Over time, this dropped debris builds up and can be a fire hazard; you won't be aware of the problem unless the chimney is inspected by a professional.
The Human Touch
While using chimney-cleaning logs is considered safe, your chimney should still be inspected and cleaned manually. Chimney sweeps are skilled at such cleaning and alert you to potential problems, such as cracks within the chimney. They will also be able to spot whether the chimney-cleaning logs have left piles of debris in an out-of-the-way area up the chimney.