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All installations and services must be performed by qualified service personnel.
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2. The return air opening may be located in the top, the center or (ideally) the bottom of the
closet door, or side wall.
: Do not obstruct any return air openings, including the return grille on the
furnace. To do so may cause the furnace to activate the high temperature limit and shutdown,
or it may cause asphyxiation.
3. The cross-sectional area of the return air duct leading into the closet (when located in the
floor or ceiling) shall not be less than 250 square inches.
4. The total free area of openings in the floor or ceiling registers serving the return air duct
system must be at least 350 square inches. At least one register must be located where it is
not likely to be covered by carpeting, boxes, furniture, or any other objects.
5. Materials located in the return duct system must have a flame spread classification of 200 or
less.
6. Pans made of a non-combustible material having 1 inch upturned flanges are to be located
beneath openings in a floor, return air, duct system.
7. Wiring materials located in the return air duct system must conform to Article 300-22 of the
latest edition of the National Electrical Code
, NFPA 70.
8. Gas piping shall not be located in, or extend through, the return air duct system.
9. Refer to section G. COMBUSTION AIR for additional combustion air requirements.
G. COMBUSTION AIR
The furnace requires the proper amount of combustion air be available to combust the fuel
cleanly and efficiently. An inadequate combustion air supply can result in unsafe and erratic
operation of the burner, sooting of the combustion chamber and the heat exchanger, and possibly,
offensive fuel odors. The combustion air intake must provide an adequate source of combustion
air to the appliance. Refer to part 5.3 of the National Fuel Gas Code
, ANSI Z223.1 / NFPA 54-
1999, or latest edition for application specific combustion air requirements.