Sub-ducts and methods of exhausting into a generally rectangular and vertical main shaft are disclosed herein. A sub-duct of one embodiment includes hollow first and second portions. The first portion presents a generally flat attaching wall, a top side that defines an opening, and a bottom side that has an aerodynamic configuration; the second portion defines an intake opening, meets with the first portion attaching wall at approximately a ninety degree angle, and has a configuration complementary to a configuration of an exhaust duct. The first and second portions collectively define a continuous channel between the intake opening and the top side opening. The first portion may have a section of generally constant cross section extending from adjacent the second portion to the top side opening, and the second portion may have a generally constant cross section extending from the intake opening to the first portion.