Combustible Floor Base Accessory; Mobile Home Filter Frame Accessories - Johnson Controls MG9S*MP Installation Manual

420705-UIM-C-0310
FLOOR BASE AND DUCTWORK INSTALLATION -
DOWNFLOW
Installations on combustible material or directly on any
floors must use a combustible floor base shown in Figure 3.
Follow the instructions supplied with the combustible floor
base accessory. This combustible floor base can be
replaced with a matching cooling coil, properly sealed to
prevent leaks. Follow the instructions supplied with the
cooling coil cabinet for installing the cabinet to the duct con-
nector. Plug intake and vent pipe holes in bottom panel and
move grommet to desired vent side exit.
Downflow Air Conditioning Coil Cabinet
The furnace should be installed with coil cabinet part number specifi-
cally intended for downflow application. If a matching cooling coil is
used, it may be placed directly on the furnace outlet and sealed to pre-
vent leakage. For details of the coil cabinet dimensions and installation
requirements, refer to the installation instructions supplied with the coil
cabinet.
Attach the air conditioning coil cabinet to the duct connector, and then
position the furnace on top of the coil cabinet. The connection to the fur-
nace, air conditioning coil cabinet, duct connector, and supply air duct
must be sealed to prevent air leakage.
DOWNFLOW DUCT CONNECTORS
All downflow installations must use a suitable duct connector approved
by the furnace manufacturer for use with this furnace. The duct connec-
tors are designed to be connected to the rectangular duct under the
floor and sealed. Refer to the instructions supplied with the duct con-
nector for proper installation. Refer to the separate accessory parts list
at the end of these instructions for the approved accessory duct con-
nectors.
FIGURE 3: Combustible Floor Base Accessory
RESIDENTIAL AND MODULAR HOME UPFLOW
RETURN PLENUM CONNECTION
Return air may enter the furnace through the side(s) or bottom depend-
ing on the type of application. Return air may not be connected into the
rear panel of the unit.
BOTTOM RETURN AND ATTIC INSTALLATIONS
Bottom return applications normally pull return air through a base plat-
form or return air plenum. Be sure the return platform structure or return
air plenum is suitable to support the weight of the furnace.
The internal bottom panel must be removed for this application.
Attic installations must meet all minimum clearances to combustibles
and have floor support with required service accessibility.
6
FURNACE
WARM AIR PLENUM
WITH 1" FLANGES
FIBERGLASS
INSULATION
FIBERGLASS TAPE
UNDER FLANGE
COMBUSTIBLE FLOOR
BASE ACCESSORY
DOWNFLOW RETURN PLENUM CONNECTION
The return air duct and the return air plenum are not required by the fur-
nace manufacturer provided the combustion air and vent system have
been installed and maintained as a Two Pipe Sealed Combustion Air
System and provided a return air duct and plenum are not required by
state, local or regional codes.
• If a return air duct system and return plenum are required by
state, local or regional codes then the return plenum may be con-
nected to the furnace inlet and must terminate outside the space
containing the furnace. The external air filter accessory shown in
Figure 4 is designed and recommended for use inside the return
plenum. Attach the return plenum to the furnace inlet duct
flanges. This is typically through the use of S cleat material when
a metal plenum is used. Installations where a return air duct sys-
tem is utilized, the use of a listed flexible duct connector is recom-
mended. The connection of the plenum to the furnace and all the
ducts connecting to the plenum must be sealed to prevent air
leakage. The sheet metal should be crosshatched to eliminate
any popping of the sheet metal when the indoor fan is energized.
The duct system is a very important part of the installation. If the
duct system is improperly sized the furnace will not operate prop-
erly. The ducts attached to the furnace must be of sufficient size
so that the furnace operates at the specified external static pres-
sure and within the air temperature rise specified on the name-
plate and in Table 3.
• If the return air duct and plenum are not required by state, local or
regional codes then the filter can be attached to the top of the fur-
nace as shown in Figure 6.
When replacing an existing the furnace, if a return air plenum is
used and the existing plenum is not the same size as the new fur-
nace, then the existing plenum must be removed and a new plenum
installed that is the proper size for the new furnace. If a return duct
mounted filter rack or filter grille is being used, see the instructions
provided with that accessory for proper hole cut size.
Downflow Filters
Downflow furnaces typically are installed with the filters located above
the furnace, extending 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.
Filter(s) may be located in the duct system external to the furnace using
an external duct filter box 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.
FIGURE 4: Mobile Home Filter Frame Accessories
Johnson Controls Unitary Products