It's block with an 8" by 8" masonary [?] flue. Flue is that brown baked looking stuff if you know what I mean.

If it is coming through the block and flue, what do I do to seal it out?

My brick chimney doesn't leak a drop.

Thanks a lot for the reply. Am at my wits end with this situation.

EDIT....Yes, it is on an outside wall.

__________________
Cheers,
Bill