Let me start by saying my chimney is located on an exterior wall on the outside of the house. We have central air, old system, we have an intake and return in every room. There is an intake right next to the chimney and another intake acroas the room.

In the winter when we light the fireplace, chimney smoke smell lingers for maybe 2 weeks. Some have attributed this because of the cold outside air cooling the chimney, and bringing the smell in... but then wouldnt the heated air in the house be carrying the smell out since hot air rises?

But more importantly, on some really hot/humid days (not all) i get the chimney smell in my living room as well. Is this again from the return next to the fireplace sucking the air from the leaky damper?

Fyi not sure if this helps any- split level home, furnace/central air in basement. Attic has a gable vent and thermo controlled fan on other gable end + ridge vents. We also have the norm kitchen exhaust/bath fan/dryer. A couple of other things of note, we have an attic bedroom that is not completely isolated from the attic space because of crappy leaky kneewall doors. Additionally we've only been in this house little over a year so some upstairs ceiling fixtures we added, and have not put actual fixtures there so the box w bare bulb is sitting there, so penetrations into attic space, with crummy like r5 1959 insulation that is pretty bare. So not sure if the attic fan is also pulling air from these.

Considering buying one of those wool fireplace damper plugs as ive heard thoae help a lot with the backdraft from fireplace, but need to see what else i have to do to eliminate problem.

Does opening basement window a crack help at all?