DAKA 521FB Manual Page 21 of 32 January 2009Rev. 2, June 2012X. INSTALLATIONA.1. CONNECTING TO DUCTWORK (SUPPLEMENTARY/ADD-ON)IMPORTANT: Installation of a cold air return line to the DAKA furnace is mandatory.IMPORTANT: The plenums installed to the furnaces must be of metal construction.Verify beforehand that sufficient clearance is available above air conditioner coil, etc. If sufficientclearance is not available, air conditioner coil may have to be moved to a second plenum with diversionbaffles for summer use.The 90° degree elbow within the supply plenum forms a venturi. This is used to extract air from theDAKA furnace when the primary furnace blower comes on. The absence of this elbow will cause backpressure down the warm air pipe to the DAKA furnace. This will adversely affect the heat distributionand possibly damage the DAKA furnace. If space prohibits installation of 90° degree elbow asrecommended, look for alternate designs shown in FIG. 20 or on Page 23. (Continued on page 22.)(EXAMPLE)FIG. 19FIG. 20(See other options on page 23)