Big Buddy is the hit of the portable unvented line of Mr. Heaters. Adjustable from 4,000 to 18,000 BTU this unit will heat up to 400 sq. ft. Comes with a 12 volt fan that operates on 4 D batteries. Operates on 2 disposable cylinders for up to 22 hours and readily adapts to bulk cylinder use. We recommend the low pressure supply hose assemble F271803. Low oxygen shut-off system and tip-over switch provided for safety. Dont forget to purchase the fan AC adapter #F276127 and your carry bag #F274889.