The air space seems fine.
I have a 12/12 flue with a proper air chamber.
I will tell you I had to raise the grate by 2.5" (with cut brick at each...
They applied the marble against the wall/brickwork with (I believe) thinset.
And I am wondering if 190 degrees is normal for the top wall area over...
I'm a newbie to the group.
I had my mason replace a gas fireplace with a real masonry wood burning one.
Opening is 40 by 29 with a 12"...
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