Many people complain about an odor that comes from their fireplaces even when a fire is not burning. Fireplace smells come from creosote deposits in the chimney; creosote is a natural by-product of burning wood. These odors are ususally worse in the summer when the humidity is high, on rainy days, and/or when the air conditioner is running. During these days a "campfire" like smell will often enter a home.
If you have a smell coming from your fireplace, it means that negative air pressure in the home is causing air from the outside to be sucked into the room. This negative air pressure can be caused by: a new furnace, new roofing, new windows, dryer operation, bathroom and kitchen exhaust fans, or other similar home improvements.