I am running black pipe out of the back of a Tarm 60. The pipe will come out the back and into a elbow and run about 5 ft at a 45 degree angle to where it will transfer to the Class A stainless coming through the roof. My question is that I assume clearence is less with class A vs black pipe. The entire room will have 5/8" plaster board for fire protection. What is the distance that black pipe can be from a protected wall if that is considered protected?