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.
Filters(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 sup- ports 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. Consid- eration should be given when locating the air cleaner for maintenance
HORIZONTAL APPLICATION
Horizontal Filters
All filters and mounting provision must be field supplied. Filters(s) may be located in the duct system external to the furnace or in a return filter grille(s). Filters(s) may be located in the duct system using an external duct filter box attached to the furnace plenum. Any branch duct (rectan- gular or round duct) attached to the plenum must attach to the vertical plenum above the filter height. The use of straps and / or supports is required to support the weight of the external filter box.
An accessory filter rack is available.
ATTIC INSTALLATION
and temperatures should the indoor fan motor fail to operate. The use of straps and / or supports is required to support the weight of the elec- tronic 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.
All loose accessories shipped with the furnace must be removed from the blower compartment, prior to installation.
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. If the furnace does not oper-
LINE CONTACT ONLY PERMISSIBLE BETWEEN LINES FORMED BY THE INTERSECTION OF FURNACE TOP AND TWO SIDES AND BUILDING JOISTS, STUDS OR FRAMING
GAS
PIPING
SUPPLY
AIR
12” CLEARANCE FOR SERVICE
COMBUSTION AIR
30” MIN.
WORK AREA
FILTER RACK
RETURN
AIR
VENT PIPE (maintain required clearances to combustible)
ate within the specified rise range then a larger air filter or an air filter that has a lower pressure drop must be installed.
IMPORTANT: For easier filter access in a downflow configuration, a removable access panel is recommended in the vertical run of the return air plenum immediately above the furnace.
| CLOSET |
COMBUSTION | RETURN |
AIR | AIR |
VENT | AIR |
PIPE | FILTERS |
ELECTRICAL
SUPPLY
GAS SUPPLY 
(EITHER SIDE)
FIGURE 4: Return Filter Grill and Return Duct Installation
FIGURE 5: Typical Attic Installation
This appliance is design certified for line contact when the furnace is installed in the horizontal left or right position. The line contact is only permissible between lines are formed by the intersection of the top and two sides of the furnace and the building joists, studs or framing. This line may be in contact with combustible material.
IMPORTANT: In either a horizontal left or right installation, a minimum of 8" (20.3 cm) clearance is required beneath the furnace to allow for the installation of the condensate trap and drain pipe. Refer to "CON- DENSATE PIPING" section of this manual for more information.
When a furnace is installed in an attic or other insulated space, keep all insulating materials at least 12 inches (30.5 cm) away from furnace and burner combustion air openings.
If this furnace is installed over a finished space, a condensate safety pan must be installed.
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. Refer to Table 19.
All installations must have a filter installed.
SUSPENDED FURNACE / CRAWL SPACE INSTALLATION
The furnace can be hung from floor hoists or installed on suitable blocks or pad. Blocks or pad installations shall provide adequate height to ensure the unit will not be subject to water damage. Units may also be suspended from rafters or floor joists using rods, pipe angle supports or straps. Angle supports should be placed at the supply air end and near the blower deck. Do not support at return air end of unit. All four sus- pension points must be level to ensure quite furnace operation. When suspending the furnace use a secure a platform constructed of plywood or other building material secured to the floor joists. Refer to Figure 6 for typical crawl space installation.
8 | Unitary Products Group |
