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, accidental tip-over safet shut-off, 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 or 12' hose. Uses A/C adapter or 4 "D" cell batteries to power blower. CSA (Canadian Standards Association) listed. Low oxygen sensor prohibits use at altitudes of 7000' or above. Heats up to 108 hours on a single 20 Lb. propane tank