What is the minimum distance a furnace chimney must be away from a wall/roof?

And does the chimney have to extend above roof peak? We are removing the old brick chimney in the center of the house and moving the furnace out of the center of the basement. The furnace will be moved to the side of the basement and the chimney will run up along the foundation up through the 1st floor and into the knee wall/attic space in the attic where it will run along the roof on about a 45 deg angle to near the peak and extend through the roof. Does this meet code or does the chimney have to be vertical.