Use kit 25B23 for installation options for the combustion air intake assembly. For 80% efficiency ultra low nox single stage and two stage upflow units only. Includes: PVC Street Elbow 2" 107621-01 Screen 105169-02 PVC Tube 2" - 102867-03 PVC Sweep Elbow 2" - 107622-01 Air Orifice - 616086-02 Air Orifice - 616086-05 Air Orifice - 616086-09 Air Orifice - 616086-11 Air Orifice - 616086-24 Air Orifice - 616086-30