ROCKWOOL COMFORTBOARD™ 80 is a rigid mineral wool insulation sheathing board that is non-combustible, water-repellent, fire-resistant and sound absorbent. Read more What are you insulating?
I have a large brick enclosure that surrounds my wood burning fireplace and when I was up in the attic I noticed that the space surrounding the fireplace between the walls is wide open to my attic. I could fit down in the space. I was spraying cellulose insulation and was about to fill in the gaps but stopped.
Soak 1/2 cup of wood chips in a bowl of water for 30 minutes to an hour. Drain and place wood chips in smoker box. If using an empty tin can instead of a smoker box, place wood chips inside tin can and cover with lid or aluminum foil. Poke holes in the lid or foil to allow smoke to escape.
Insulating with rock-wool batting in the studs/joist/rafter bays is preferable to fiberglass, and foam (particularly polystyrene foam) with just the 2" clearance would be a bit insane, even if it meets the letter of code. When going through a foam layer, use 3" or more of rock wool between the flue's 2" clearance zone and the foam.
When installing a fireplace, insulation should be a priority and not an afterthought. Whether installing a Heatilator gas fireplace or another brand, you will need to make an assessment of the insulation currently in your walls and determine if more is needed, but you cannot have insulation along the entire chimney and fireplace.
ROCKWOOL provides a suite of insulation products for all floor and ceiling applications, including ground, separating and intermediate floors, which not only perform acoustically and thermally - they are also A1 non-combustible to offer a greater level of fire protection.