The C199 Commercial High-Efficiency Tankless Water Heater achieves the highest standards of reliability and efficiency. This 96% thermal efficiency Tankless Water Heater comes standard on the Tankless Rack System™ (wall mount or free-standing) and is also available in individual units. Available in natural gas or propane, the C199 is a dedicated commercial tankless model, precision engineered to produce an endless supply of hot water for even the most demanding applications - from restaurants to hotels to multifamily residences to schools and more. When the demands are greatest, Rinnai® delivers.