Rinnai Endless Hot Water TANKLESS WATER HEATER Exterior Unit For Use With NATURAL GAS Model # R63LSE-NG Continuous Hot Water On Demand Delivered at Up to 6.3 GPM. MC-91 Digital Temperature Controller +/-2 F Included. * Direct Electronic Ignition - No Pilot Light On-Board Diagnostics And Safety Monitoring. * Exterior Unit - No Venting Required. Battery Backup Possible for Operation in Power Interruptions. EZ Connect (connects 2 units together without need of additional control board).