The SENSEI RX199iN condensing tankless water heater from Rinnai is only the size of a small suitcase, uses either Natural Gas or Propane, and can be installed indoors or outdoors using the Versa-Vent accessory. Rinnai SENSEI RX Series tankless water heaters last up to twice as long as tanks and have twice the warranty length. Plus, they save energy by heating water only when it is needed.