I have a Heat-n-glo gas fireplace I'm installing in a remodel. It vents straight up through the ceiling and then through the roof. There's about 1 foot from the ceiling to where it passes through the roof...this is the attic space. I boxed out with 2x6 around the flue and installed a metal firestop on the top portion (10" x 10"). So, from the inside looking up, you can see the 2x6 box and firestop. The drywall goes up to the box I made. Above the firestop is blown insulation, but none of it is touching the flue...that I know about.

So, is this all acceptable code wise? Do they usually drywall up to the flue on the inside? Seems like a lot of heat could escape up and through that area since there is no insulation. Does the drywall need to be taped and mudded at the seams?

I live in Minnesota.