18-28-918.9.4.1.

   A furnace plenum supplied as a part of a furnace shall be installed in accordance with the manufacturer's instructions.

18-28-918.9.4.2.

   Where a furnace plenum is not supplied with the furnace, any fabrication and installation instructions provided by the manufacturer shall be followed. The method of connecting supply and return ducts shall facilitate proper circulation of air.

18-28-918.9.4.3

   Where a furnace is installed so supply ducts carry air circulated by the furnace to areas outside the space containing the furnace, the return air shall also be handled by a duct(s) sealed to the furnace casing and terminating outside the space containing the furnace.

18-28-918.9.5 Combustion and circulating air.

18-28-918.9.5.1.

   Combustion and circulating air shall be provided in accordance with Article 7, Combustion Air.

18-28-918.9.6 Furnace plenums and air ducts.