Brick Bell Through a Wall: Clearance

I am considering building a masonry bell through the wall between my dining room and kitchen. There is already a hole in the framing from a former window (living room was added on after the house.) So it would be easy enough to re-open the hole and expand it to the floor level. But it is timber framed so it needs careful consideration for safety.

Would making the bell with 2 inches of clearance all around be enough? I figure the hole will need to be trimmed/capped in tin as well. How else would you go about protecting the frame from heat?  

Brick bell ? Double layer ?

Thickness of the stud wall? About 8 or 10 inches ? Less ? If not over 10 inches, a gap of two inches should plenty. But not up to code in some areas. Where i live, you would need 18cm all around, if it is considered as a flue.

One idea popped into my head. You could also line the framing edge with U channel beams to cut whatever high heat might radiate from the bell. Mind you, mine, on a batch only goes to 60 celcius outer skin, on the coldest days, when the stove roars like mad.