The Rinnai 223186PP Concentric Venting Condensing Horizontal Termination Diverter Kit is an additional component of a Concentric Venting accessory. A Concentric Venting accessory is frequently used to turn a two-vent system into a single exiting vent. It also slightly warms the air before it reaches the heating part of your Rinnai Tankless Water Heater. This accessory is specifically design for Rinnai's Condensing Tankless Water Heaters.