Section 27-892. Construction

Vent connectors for conversion burners without
  draft hoods, or other gas-fired equipment without draft hoods, shall  be
  constructed  of materials having resistance to corrosion and temperature
  not less than that of no. 24 galvanized sheet gauge steel.
    (a) Vent connectors used for gas-fired equipment  having  draft  hoods
  and  for  conversion burners having draft hoods, shall be constructed of
  type B gas vent material or materials having resistance to corrosion and
  temperature not less than that of no. 26 galvanized sheet gauge steel.
    (b) The vent connector between the equipment and the vertical gas vent
  or chimney shall have the greatest possible initial rise consistent with
  the headroom available in the  equipment  area  and  with  the  required
  clearance  to  combustible  material.  The  horizontal  run  of the vent
  connector shall be as short as  possible  and  the  equipment  shall  be
  located  as  near  the  gas  vent or chimney as practicable. The maximum
  length of an uninsulated horizontal run  of  vent  connector  shall  not
  exceed seventy-five percent of the height of the gas vent or chimney.
    (c)   No   vent   connector   shall  pass  through  floor  or  ceiling
  construction.