What is the vent to outside near your fireplace and how does it work?
IF you have a woodburning fireplace, and there is a small door-
about 6 inches square on the outside of the house, check for a flip
open door on the floor of your fireplace. If that is what you have,
this is not a vent, but an ash clean-out. Shovel ashes thru the
door on the floor of the fireplace, and you can remove them from
the outside door without making a mess in the house. But not a
vent. If that is not what you have, please post gain with a more
detailed description.