Stove pipe is used for venting wood-burning stoves and is used inside the room where the stove is installed.
As soon as that pipe goes through a ceiling (upstairs floor) it must be converted to a Class A chimney pipe.
If stove pipe is used outside, it will not be able to maintain sufficient temperature to prevent creosote build up so the risk of a chimney fire is increased.
Class A chimney pipe requires 2 inches of clearance to combustibles.
Fire -> stove pipe -> ceiling support box/ round ceiling support piece -> Class A