Indoor safe propane heater. Mr. Heater Big Buddy radiant heater provides safe heat for chilly garages, tents, patios, porches, cabins, etc. 3 heat settings: 4000, 9000, or 18,000 BTU (British thermal unit). It has been designed and approved for indoor use. Features include built-in protection probe, easy carry handle, automatic low oxygen shut off system, blower fan, power On/Off switch, large 4 position heat level control knob with built-in piezo starter, integrated. Quiet,odor-free, lightweight, and portable. Uses 1 or 2 one lb propane cylinders or larger tank with optional 5' hose (SKU 424633) or 12' hose (SKU 425435). Uses A/C adapter (SKU 445753) or 4 "D" cell batteries to power blower. 17" L x 10" W x 17-1/2" H. CSA (Canadian Standards Association) listed. Heats up to 500 sq ft (square foot). Low oxygen sensor prohibits use at altitudes of 7000' or above.