The I- Series i120SN model features Rinnai's exclusive self-cleaning stainless-steel heat exchanger coupled with a secondary flat plate heat exchanger. This heat-only model can deliver whole house heating to enhance your comfort. This model provides an input rating of 120K Btu. Fueled with either Natural Gas or Propane this Rinnai condensing gas boiler has obtained one of the highest AFUEs (Annual Fuel Utilization Efficiency) in the industry. Plus, the compact wall-mounted design saves space over traditional boilers.