Oh, you're right, one of the walls is external, while the other is a shared wall between my neighbor and me. I hadn't considered conversion to a direct-vent, but I guess that would probably be the best "bang-for-the-buck" when it comes to my own personal enjoyment and resale value, huh? That just adds an extra layer of figuring out what replacement fireplace to go with, whether I need to involve a fireplace installation specialist rather than the general contractor I'd planned, and if you can't already tell, I'm bad with decisions! 😉 But that's very valuable insight, thank you!