Generac 6721 Guardian Series, 16kW Air Cooled Standby Generator, Natural Gas/Liquid Propane Powered, Aluminum Enclosed (Discontinued by Manufacturer) Runs on Natural Gas or Liquid Propane and features hands-free operation with no manual start, no fueling, and no extension cords True Power Technology Guarantees Less than 5% Total Harmonic Distortion, Keeping your Sensitive Electronics Safe Operation requires automatic transfer switch (not included) UL, CUL, and EPA Compliant for Safety 5-Year, Limited Warranty from Generac is included