The Econo Outdoor Wood Furnace is built of quality material by Missouri craftsmen in the USA. The water tank is 11 gauge steel, the fire box is 9 gauge steel, with a 6 inch X ¼ inch flue pipe that runs vertical out the top of the fire box through the water tank then out to the atmosphere.The Econo Outdoor Wood Furnace has a large firedoor to allow big pieces of wood to be burned without splitting.The Econo Outdoor Wood Furnace comes standard with a three (3) year warranty against defects and workmanship.