Mr. Heater Model: F232017 4,000- to 9,000-BTU radiant heater for spaces up to 225 square feet. Approved for indoor/outdoor use; clean-burning; nearly 100-percent efficient When operating the heater at altitudes over 7,000 FT above sea level the heater may shut off. Auto shut-off if tipped over, if pilot light goes out, or if detects low oxygen levels Uses small camping propane tanks, or can purchase a hose and connect larger tanks (such as 20lb grill tanks) to it.