INSTALLATION CONSIDERATIONS
15
(c)
The minimum size of outdoor opening(s) shall be the full size
of outdoor opening(s) calculated in accordance with 9.3.3,
multiplied by the reduction factor. The minimum dimension
of air openings shall not be less than 3 in. (80 mm).
9.3.5 Engineered Installations.
Engineered combustion air installa-
tions shall provide an adequate supply of combustion, ventilation, and
dilution air and shall be approved by the authority having jurisdiction.
9.3.6 Mechanical Combustion Air Supply.
Where all combustion air
is provided by a mechanical air supply system, the combustion air shall
be supplied form outdoors at the minimum rate of 0.35 ft
3
/min per
1000 Btu/hr (0.034 m
3
/min per kW) for all appliances located within
the space.
9.3.6.1
Where exhaust fans are installed, additional air shall be provided
to replace the exhausted air.
9.3.6.2
Each of the appliances served shall be interlocked to the me-
chanical air supply system to prevent main burner operation where the
mechanical air supply system is not in operation.
9.3.6.3
Where combustion air is provided by the building’s mechanical
ventilation system, the system shall provide the specified combustion
air rate in addition to the required ventilation air.
9.3.7 Louvers, Grilles, and Screens.
9.3.7.1 Louvers and Grilles.
The required size of openings for com-
bustion, 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 size opening
required to provide the free area specified. Where 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 louvers and grilles shall be
fixed in the open position.
9.3.7.2 Minimum Scree Mesh Size.
Screens shall not be smaller than
1/4 in. mesh.
9.3.7.3 Motorized Louvers.
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.
9.3.8 Combustion Air Ducts.
Combustion air ducts shall comply with
9.3.8.1 through 9.3.8.8.
9.3.8.1
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 fireblock is removed.
9.3.8.2
Ducts shall terminate in an unobstructed space, allowing free
movement of combustion air to the appliances.
9.3.8.3
Ducts shall serve a single space.
9.3.8.4
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 main-
tained to the source of combustion air.
9.3.8.5
Ducts shall not be screened where terminating in an attic space.
9.3.8.6
Horizontal upper combustion air ducts shall not slope down-
ward toward the source of combustion air.
9.3.8.7
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 fireplace where installed in accordance with the
manufacture’s installation instructions.
9.3.8.8
Combustion air intake openings located on the exterior of the
building shall have the lowest side of the combustion air intake open-
ings located at least 12 in. (300 mm) vertically from the adjoining grade
level.
Horizontal Applications and Considerations
Horizontal applications, in particular, may dictate many of
the installation’s specifics such as airflow direction, duct-
work connections, flue and/or combustion air pipe connec-
tions, etc. The basic application of this furnace as a hori-
zontal furnace differs only slightly from an upright installa-
tion.
Horizontal Installations
1. Horizontal installations require 5.5" under the furnace
to accommodate the drain trap.
2. Horizontal furnaces must be installed with ¾” slope from
back to front to permit condensate flow towards the
front of the furnace.
When installing a *MEC96 horizontally with the left side
down, there are two options for connecting the vent pipe to
the furnace.
1. Venting may be connected to the furnace vent pipe fit-
ting 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.
