My wife and I just moved into a 15-or-20-year-old house that has two fireplaces. Her allergies have been in overdrive ever since we moved in, even with an air purifier running next to the bed at night. I finally got some thin plastic wrap and taped it over the fireplace openings, and now I'm seeing the plastic billowing a bit on one of the fireplaces and the other fireplace is sucking the plastic against the metal screen/grate, so it seems like the fireplaces aren't closed/sealed. That said, I'm trying to figure out how to do this. There's a square key hole next to each fireplace and some kind of large key that fits into it, but I don't know if this is supposed to turn on gas, or light something, or if it controls the opening in the chimney or what. If anyone can give me a little insight into how I would go about sealing/closing the chimney (at least until after allergy season), I would GREATLY appreciate it! Thank you!