Just curious, is your chimney on the main or upper level?

1st (and only) floor.
I have a
fireplace in a basement rec-room, and have assumed heatloss wasn't too bad,
since it is in a basement. Maybe I should re-think that.



You would if you saw this film moving around. Today is only mildly
breezy, and the film just never stops moving.

Tape a sheet of newspaper from the top edge & let it hang down across
the fireplace opening. I'd bet that newspaper never stops swaying around.