I have a gas log fireplace that I use seldomly. My damper was warped
and not working well just because it was old overused. The glass door
helped some, but the fireplace was still drafty and cold in the
winter. I tried a few things to plug the chimney but I bought a Chimney
Balloon online from this place in Wisconsin www.chimneyballoon.us

I did try stuffing some fiberglass before i tried the balloon, but that
was pretty itchy to remove when I wanted a fire. I probubly use it 6
times in a winter, when company is over.