I just finshed an out door fire place. It is completely encased in field stone. The fire box is square 4x4x4 with an 8x12x8 stack in the back of the box. I am not getting enough draw. The smoke is coming out the front as much as the chimney.The original had a 4 ft chimney and I added 4 more temporary ft and it still smokes.
not sure what.....with an 8x12x8 stack in the back of the box......is but what I would suggest is to open the damper, and stick 1-2 piece's of news paper up and light it the poke it through the damper and let it burn then see if it draws, it should. with an out side fireplace you have no real temp difference but if you heat up the flue and smoke chamber it should draw. If not have the local building department check to see if it was built to local codes. that might be the problem too.