What do I do if my fireplace smells?

The smell is most likely due to a natural byproduct of woodburning called creosote. Typically, the smell will be worse in the summer when the humidity is at an all-time high. There could be air pressure issues in your home that are causing air to be drawn down the chimney and into your living area. A sweeping will help but may not solve the problem entirely. A tight sealing, top-mounted damper will help because it reduces the airflow coming down the chimney.

Source: Chimney Sweep Raleigh NC | Chimney Sweep Charlotte NC