Section 27-888. Gas vent height and locations

Gas vents shall extend at
  least two feet above the highest construction, such  as  a  roof  ridge,
  parapet  wall,  or penthouse, within ten feet of the vent outlet whether
  the construction is on the same building as the chimney  or  on  another
  building.  However,  such constructions do not include chimneys or other
  vents, or open structural framing. The vent shall be  as  high  as  such
  construction  which  is  located beyond ten feet from the vent and up to
  and including the distance determined by the following formula:
 
                               D = 2(sq.rt.)A
 
  where: D = Distance in ft., measured from the center of the vent  outlet
               to the nearest edge of the construction.
         A = Free area, in sq. in., of vent flue space.
 
    Vents shall be subject to the following additional requirements:
    (a) No gas vent shall terminate less than five feet in vertical height
  above the highest connected equipment draft hood outlet or flue collar.
    (b)  No  type  B-W  gas  vent  serving  a vented recessed heater shall
  terminate less than twelve feet in vertical height above the  bottom  of
  the heater.
    (c)  All  gas vents shall terminate in an approved vent or cowl, which
  shall prevent down drafts and prevent rain and debris from entering  the
  vent.