1) The Smelly Dormant Livingroom Fireplace
This smelly fireplace is due to your clothes dryer, bathroom vent fan, and other appliances exhausting air to the outside. This creates a negative air pressure inside the home that is causing the fireplace chimney to draw in outside air (See Diagram). When a chimney breathes in like this it drags in all of the odor associated with the cresote and ash deposits in the chimney.
How to Fix It Step By Step:
Step 1: Follow the instructions to measure your fireplace
Step 2: Order a Chimney Balloon that fits your fireplace
Step 3: When the Chimney Balloon arrives, you inflate the Chimney Balloon into place to seal the fireplace low and tight. This will force the home to find another location to intake air. If you have an ash cleanout in this fireplace it is important to tightly seal that off as well. (See Q&A below)