Required for cascade/common vent installations with NPE-2, NFC-H, NFB-H and NHB (NHB-110 and NHB-150 models) Series units produced on or after September 15, 2016. Includes cascade cable (GXXX000546), VID jumper cable and common vent collar damper.
Navien Common Vent Collar Kit
Instruction/Installation Manual