268882-UIM-A-0407
8
Unitary Products Group
Downflow furnaces typically are installed with the filters located above
the furnace. If a return air plenum is used, the filter rack is installed into
the return air plenum or duct. Any branch duct (rectangular or round
duct) attached to the plenum must attach to the vertical plenum above
the filter height. Refer to Figure 7. Filters(s) may be located in the duct
system external to the furnace using an external duct filter box which
may be attached to the furnace plenum or at the end of the duct in a
return filter grille(s). The use of straps and/or supports is required to
support the weight of the external filter box.
If the accessory electronic air cleaner is installed, be sure the air
cleaner is designed to accommodate the furnace CFM (cm/m) and the
air cleaner is installed so it does not obstruct the return airflow. Clear-
ance consideration should be given when locating the air cleaner for
maintenance. The use of straps and/or supports is required to support
the weight of the electronic air cleaner. It is recommended that the air
cleaner not be located within 12 inches (30.5 cm) from the top of the
return air opening on the furnace. Refer to the instructions supplied with
the electronic air cleaner.
If pleated media air filters or any filter that has a large pressure drop is
installed in the return air duct system, be sure that the pressure drop
caused by the air filter will not prevent the furnace from operating within
the rise range specified on the rating plate and in Table 5. If the furnace
does not operate within the specified rise range then a larger air filter or
an air filter that has a lower pressure drop must be installed. Refer to
the furnace accessories for accessory external filter kit options.
IMPORTANT:
For easier filter access in a downflow configuration when
a return air plenum is being used, a removable access panel is recom-
mended in the vertical run of the return air plenum immediately above
the furnace.
IMPORTANT:
Air velocity through throwaway type filters must not
exceed 300 feet per minute (91 m/min). All velocities over this require
the use of high velocity filters.
SECTION IV: GAS PIPING
GAS SAFETY
IMPORTANT:
Plan your gas supply before determining the correct gas
pipe entry. Use 90-degree service elbow(s), or short nipples and con-
ventional 90-degree elbow(s) to enter through the cabinet access holes.
GAS PIPING INSTALLATION
Properly sized wrought iron, approved flexible or steel pipe must be
used when making gas connections to the unit. If local codes allow the
use of a flexible gas appliance connection, always use a new listed con-
nector. Do not use a connector that has previously serviced another gas
appliance.
Some utility companies or local codes require pipe sizes larger than the
minimum sizes listed in these instructions and in the codes. The furnace
rating plate and the instructions in this section specify the type of gas
approved for this furnace - only use those approved gases. The instal-
lation of a drip leg and ground union is required. Refer to Figure 9.
IMPORTANT:
An accessible manual shutoff valve must be installed
upstream of the furnace gas controls and within 6 feet (1.8 m) of the fur-
nace.
The furnace must be isolated from the gas supply piping system by
closing its individual external manual shutoff valve during any pressure
testing of the gas supply piping system at pressures equal to or less
than 1/2 psig (3.5 kPa).
All loose accessories shipped with the furnace must be removed
from the blower compartment, prior to installation.
FIGURE 7:
Modular Home Return Filter Grill and Return Duct
Installation
All installations must have a filter installed.
COMBUSTION
AIR
VENT
PIPE
ELECTRICAL
SUPPLY
GAS SUPPLY
(EITHER SIDE)
CLOSET
RETURN
AIR
AIR
FILTERS
An overpressure protection device, such as a pressure regulator,
must be installed in the gas piping system upstream of the furnace
and must act to limit the downstream pressure to the gas valve so it
does not exceed 0.5 PSI (14" w.c. (3.48 kPa). Pressures exceeding
0.5 PSI (14” w.c. (3.48 kPa) at the gas valve will cause damage to
the gas valve, resulting in a fire or explosion or cause damage to
the furnace or some of its components that will result in property
damage and loss of life.
FIGURE 8:
Convertible Gas Valve
FIGURE 9:
Downflow Gas Piping
INLET
WRENCH
BOSS
INLET
PRESSURE
PORT
ON/OFF SWITCH
(Shown in OFF position)
MAIN REGULATOR
ADJUSTMENT
OUTLET
OUTLET
PRESSURE
PORT
VENT PORT
OFF
ON
EXTERNAL MANUAL
SHUTOFF VALVE
TO GAS
SUPPLY
TO GAS
SUPPLY
GROUNDED JOINT UNION
MAY BE INSTALLED
INSIDE OR OUTSIDE UNIT.
DRIP
LEG
