SYSTEM OPERATION
13
Each of the appliances served shall be interlocked to the
mechanical air supply system to prevent main burner operation
where the mechanical air supply system is not in operation.
Where combustion air is provided by the building’s me-
combustion air rate in addition to the required ventilation air.
The required size of openings for
combustion, ventilation, and dilution air shall be based on the net
free area of each opening. Where the free area through a design
of louver or grille or screen is known, it shall be used in calculating
the louver and grille design and free area are not known, it shall be
assumed that wood louvers will have 25 percent free area, and metal
louvers and grilles will have 75 percent free area. Nonmotorized
Screens shall not be smaller
than 1/4 in. mesh.
Motorized louvers shall be interlocked
with the appliance so they are proven in the full open position prior
to main burner ignition and during main burner operation. Means
shall be provided to prevent the main burner form igniting should the
louver fail to open during burner startup and to shut down the main
burner if the louvers close during burner operation.
Combustion air ducts shall comply
with 9.3.8.1 through 9.3.8.8.
Ducts shall be constructed of galvanized steel or a material
having equivalent corrosion resistance, strength, and rigidity.
Exception: Within dwellings units, unobstructed stud and joist spaces
shall not be prohibited from conveying combustion air, provided that
not more than one reblock is removed.
Ducts shall terminate in an unobstructed space, allowing
free movement of combustion air to the appliances.
Ducts shall serve a single space.
Ducts shall not serve both upper and lower combustion
air openings where both such openings are used. The separation
between ducts servicing upper and lower combustion air openings
shall be maintained to the source of combustion air.
Ducts shall not be screened where terminating in an attic
space.
Horizontal upper combustion air ducts shall not slope down-
ward toward the source of combustion air.
The remaining space surrounding a chimney liner, gas vent,
special gas vent, or plastic piping installed within a masonry, metal,
or factory built chimney shall not be used to supply combustion air.
Exception: Direct vent appliances designed for installation in a
solid fuel-burning replace where installed in accordance with the
manufacture’s installation instructions.
Combustion air intake openings located on the exterior of
the building shall have the lowest side of the combustion air intake
openings located at least 12 in. (300 mm) vertically from the ad-
joining grade level.
left or right side down. *CEC96 models may be installed down
any furnace on its back.
Horizontal applications, in particular, may dictate many of
The basic application of this furnace as a horizontal furnace
1. Horizontal installations require 5.5” under the furnace to
accommodate the drain trap.
2. Horizontal furnaces must be installed with ¾” slope from
of the furnace.
When installing horizontally with the left side down, there
are two options for connecting the vent pipe to the furnace.
on the original top (now the end) of the furnace
2. The internal vent pipe and elbow may be removed from
the furnace to permit the vent to exit the top (original side)
of the furnace. If this option is used, an RF000142 Vent-
Drain coupling must be used to keep condensate from
collecting in the inducer assembly
Refer to the following instructions and illustration.
Insert flange. Cut 2 ½” long.
R 000142F
Figure 9
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