I've got a spot by a fireplace that lets cold air in. Unfortunately its right where the metal of the fireplace meets the wooden framing/molding of the fireplace on the inside. This seems like something I should be able to take care of. Its a rather sizable gap (maybe 3/4 of an inch). I didn't think I could caulk such a large gap. I wanted to use some kind of spray insulation such as "Great Stuff", but the label indicates that its flamable (not to mention highly toxic and needs to be covered).
What should I do to cover this gap and prevent air flow in a way that's safe and effective?
With regards to sealing outside
Unfortunately I can't seal the outside without great expense. My home energy auditor has said that its likely that the area surrounding the fireplace is not insulated. He has told me that it would be expensive to gain access to the gap between each stud and blow in insulation.
He suggested sealing the crack on the inside as the most cost effective way to improve the comfort in this room. When he came and used his IR camera, the spot on the floor next to this gap was in the 30's in temperature.
There's a gap between black slate(?) of fireplace and white wooden fireplace frame.