Section 27-884. Types of gas vents

(a) Type B gas vents. Type B gas vents
  conforming to the requirements of section 27-855 of article one of  this
  subchapter may be used to vent gas-fired equipment. Type B gas vents may
  be  used for single-story or multi-story installations when they conform
  to the requirements of section 27-855 of article one of this  subchapter
  and  the  gas  equipment  used  in  multi-story  installations  shall be
  accepted for such use. Type B gas vents  shall  be  used  to  vent  only
  listed  gas  appliances with draft hoods and other gas appliances listed
  for use with Type B gas vents. However, Type B gas vents  shall  not  be
  used for venting:
    (1) vented wall furnaces listed for use with Type BW gas vents only;
    (2) incinerators;
    (3)  appliances  which may be converted readily to the use of solid or
  liquid fuels;
    (4) combination gas-oil burning appliances;
    (5) appliances listed for use with chimneys only.
    (b) Type  B-W  gas  vents.  Type  B-W  gas  vents  conforming  to  the
  requirements  of  section 27-855 of article one of this subchapter shall
  be used to vent gas-fired vented recessed heaters. Type  B-W  gas  vents
  may  be  used  with  single-story or multi-story installations when they
  conform to the requirements of section 27-855 of  article  one  of  this
  subchapter and the gas equipment used in multi-story installations shall
  be accepted for such use. Type BW vents shall be used with listed vented
  gas  wall furnaces having a capacity not greater than that of the listed
  Type BW gas vent.
    (c) Single-wall metal vents. Single-wall metal vents may  be  used  to
  vent  gas-fired  equipment  and shall be constructed of not less than 16
  oz.  sheet copper, or No. 20 galvanized sheet gauge steel, or  of  other
  equivalent   noncombustible  corrosion-resistive  material.  Single-wall
  metal gas vents may pass through  the  roof  or  exterior  wall  to  the
  outdoor  air,  but  shall  not pass through any attic or other concealed
  space nor through any intermediate floor construction.
    (d) Connection to a common vent. Connection of gas-fired equipment  on
  more  than  one  floor level to a common vent, except as provided for in
  subdivisions (a) and (b) of this section, shall be prohibited.
    (e) Ventilating hoods. Ventilating hoods and exhaust  systems  may  be
  used to vent kitchen, laboratory, and commerical equipment.