PRODUCT DESCRIPTION Rinnai RCi Series Tankless Water Heaters utilize concentric venting with an inner pipe that is designed to withstand varying flue temperature conditions that may be experienced over the life of a condensing product. The Ubbink Rolux condensing concentric vent system is considered part of the direct vent tankless water heater, and has been tested and approved with the appliance by a third party testing agency. FROM THE MANUFACTURER Rinnai RCi Series Tankless Water Heaters utilize concentric venting with an inner pipe that is designed to withstand varying flue temperature conditions that may be experienced over the life of a condensing product. The Ubbink Rolux condensing concentric vent system is considered part of the direct vent tankless water heater, and has been tested and approved with the appliance by a third party testing agency.