I ran the fireplace for a while with it sitting outside the hole and it was still very cool to the touch all around. In fact even the part where the heater is was cool, it only gets hot directly in front of the heater, when it's on. The fireplace is more for show than anything. Ended up going with the foam as realized it's already a tight fit as is so would not have room for batts and I'd still have to put a vapor barrier while the foam acts as one. Waiting for caulk to dry then I'll add the vapor barrier tape. I might be able to throw some fiberglass batts in the back though and I might be able to squish it against the sides if there's still some wiggle room.
I'll definitely keep an eye on it for the first time I turn it on though.
At least that's one cold source less to worry about. Only like R3 though but think the air seal is probably more important than anything in this case. The brick probably adds some R value too, very small, but some.
If ever I decide to get a gas fireplace there, then I'd probably have to redo that whole area.
edit: Taped up!
Now a fireplace that does not make my house colder... lol
Of course with my luck it warmed up quite a bit so I'll have to wait and see how good of a job I did when it gets cold again. It's 0 right now, imagine that.
Last edited by Red Squirrel; 01-28-2013 at 10:26 PM.