AAA Outdoor Boiler Outdoor Wood/Coal Gasification Boiler - 160,000 BTU, Model# Reburn R-120 Unique gasification boiler with 120-gallon capacity 1/4in. thick firebox Fill firebox every 12-16 hours Water jacket (1/8in. on top and all four sides, 3/16in. bottom) All six sides of firebox, plus flue pipe inside, sides of ash pan and back of furnace are totally surrounded with water to capture all of the heat