Usually, the smell coming from your chimney is caused by a buildup of creosote, soot, or other debris. Additionally, rainy days will add moisture and produce an unpleasant smell from your dirty chimney. An inspection and sweep is a good place to start for a smelly chimney because it will remove excess creosote and rule out other common problems that may have caused the smell. During the cleaning, other debris will be removed thus eliminating these options as a cause for the smell.
Common causes of a smelly chimney include water seeping into the chimney and negative air pressure. Having a well-functioning chimney cap will prevent water damage issues. Solving the water issue is relatively simple, but the negative air pressure can be a bit more complicated. Pinpointing what is causing negative air pressure is the tricky part. The change in pressure could be due to changes that you make in your home such as new furnace installation. To correct the negative air pressure issue, you can do a couple of things including:
Humid summer days and rainy days adding moisture will produce undesirable odors from a dirty chimney. Having your chimney cleaned will dispose of any decomposing materials and will also clean the creosote out of the chimney. If the chimney cleaning and inspection don’t get rid of the odor, the next course of action would be to seal the chimney from water sitting in the chamber and causing a musty smell. Adding a chimney cap to your chimney will keep water, debris, and animals out of your chimney. Below is a list of what your chimney might smell like with what is most likely causing that smell.
Animals entering your chimney and not being able to escape
Fallen leaves combining with damp soot
Water sitting in your smoke chamber
Most likely due to creosote buildup