211. Tilt or raise furnace and remove 4 screws holding bottomplate. (See Fig. 22.)2. Remove bottom plate.3. Remove bottom closure panel.4. Reinstall bottom plate and screws.Side Return Air InletThese furnaces are shipped with bottom closure panel installed inbottom return--air opening. This panel MUST be in place whenside return air inlet(s) are used without a bottom return air inlet.Not all horizontal furnaces are approved for side return airconnections (See Fig. 26.)Filter ArrangementFIRE, CARBON MONOXIDE AND POISONINGHAZARDFailure to follow this warning could result in fire, personalinjury or death.Never operate a furnace without a filter or filtration deviceinstalled. Never operate a furnace with filter or filtrationdevice access doors removed.! WARNINGFOR FURNACES SHIPPED WITH AMEDIA CABINETThere are no provisions for an internal filter rack in these furnaces.An external filter is required.The furnace is shipped with a factory-supplied Media FilterCabinet. The Media Filter Cabinet uses either a standard 1-in. (25mm) filter or 4-in. (102 mm) wide Media Filter which can bepurchased separately. A field supplied accessory air cleaner mayalso be used in place of the media cabinet.The Media Cabinet is sized for bottom return applications for usein upflow, downflow and horizontal applications. A 16--in. (406mm) Media Cabinet is shipped with the 14--3/16-in. (360 mm)furnace and includes block-off platesFor upflow side return applications, the Media Cabinet (or fieldsupplied accessory air cleaner) can be installed on the side of thefurnace or side and bottom when a bottom plenum is used. (SeeFig. 18 and 24.)For downflow applications, the Media Cabinet (or field suppliedaccessory air cleaner) must only be connected to the bottomopening on the furnace. See Fig. 18 and 25.For horizontal applications, the Media Cabinet (or field suppliedaccessory air cleaner) for all models can be connected to thebottom opening on the furnace. For side return use in thehorizontal position, refer to Fig. 26. If both side and bottomopenings are used in Fig. 26, each opening used will require afilter.The media cabinet (or field supplied accessory air cleaner) can alsobe installed in the common return duct prior to entering the returnair opening in any orientation.Refer to the instructions supplied with Media Cabinet or accessoryair filter for assembly and other details.See Table 5 for filter size details.Table 5 – Filter Size Information -- In. (mm)FURNACE CASING WIDTH FILTER SIZE FILTER TYPESIDE RETURN BOTTOM RETURN14--- 3/16{ (360) 16 x 25 x 3/4(406 x 635 x 19)14 x 25 x 3/4(356 x 635 x 19) Washable*17--- 1/2 (445) 16 x 25 x 3/4(406 x 635 x 19)16 x 25 x 3/4(406 x 635 x 19) Washable*21 (533) 16 x 25 x 3/4(406 x 635 x 19)20 x 25 x 3/4(508 x 635 x 19) Washable*24--- 1/2 (622) 16 x 25 x 3/4(406 x 635 x 19)24 x 25 x 3/4(610 x 635 x 19) Washable** Recommended to maintain air filter face velocity. See Product Data for part number.{ Not all families have these models.Air Filter Located in Filter CabinetFILTER CABINET HEIGHT --- IN (MM) FILTER SIZE --- IN (MM) FILTER TYPE16 (406)(1) 16 x 25 x 3/4*(406 x 635 x 19) or(1) 16 x 25 x 4--- 5/16(406 x 635 x 110)Washable or Media*20 (508)(1) 20 x 25 x 3/4*(508 x 635 x 19) or(1) 20 x 25 x 4--- 5/16(508 x 635 x 110)Washable or Media*24 (610)(1) 24 x 25 x 3/4*or(610 x 635 x 19) or(1) 24 x 25 x 4--- 5/16(610 x 635 x 110)Washable or Media** Filters with a side return ---air may have a different filter size. Measure the filter to obtain the correct size.* Recommended to maintain air filter face velocity. See Product Data for part number.59SP5A