Rheem RRTG20151A-1-1 90-Degree Elbow Gas VentingAll indoor tankless gas water heaters must be vented vertically or horizontally to the outdoors using factory approved venting material (No other venting material is permitted). See the Use and Care Manual for important information regarding the venting installation and materials for your tankless water heater. NOTE: Rheem outdoor tankless water heaters do not require venting materials. Rheem RRTG20151A-1-1 90-Degree Elbow Gas Venting Features: 8.1" rise 8.1" run MF3CG90L Model: RTG20151-A Rheem offers many venting accessories to make your tankless water heater installation easy. Replaces: Rheem RTG20151A