can it be converted to natural gas??
well, this is from their (Rinnai) web sight... looks like it might be rather difficult to change to Natural Gas.
Can a Rinnai Tankless Water Heater be converted to a different gas type?
Rinnai offers a limited Field Conversion Program. Kits for converting gas tankless water heaters from natural gas to propane or vice versa are available for most models. Please have your installer/service provider call 1-800-621-9419 to find out if your model qualifies and to obtain a detailed step-by-step conversion instruction kit.
These kits are available directly from Rinnai, and will be shipped only after the installer/service provider has contacted Rinnai’s technical support services and consulted one of our technical specialists, to ensure the installer/service provider performing the conversion is qualified to do so. The Field Conversion Program is available for products which have been installed and where gas type availability has changed. It will not be approved for use in conversion of non-sold inventory or mobile homes.