A furnace includes a decomposition chamber configured to form a fire pit for controlled decomposition of combustible waste material, a preheat chamber connected to and located generally above the decomposition chamber, and an afterburn chamber operably connected to an outlet on the decomposition chamber. The decomposition chamber includes an inlet for allowing controlled input of air to the decomposition chamber to create an oxygen-starved environment. The outlet is positioned generally opposite the inlet on the decomposition chamber and adjacent the fire pit such that the gases from the preheat chamber and the decomposition chamber flow generally across the decomposition chamber and through the burning/decomposing waste materials in the fire pit. The afterburn chamber chamber operates with a vacuum such that the gases and vapors from the preheat chamber and the decomposition chamber are drawn through the fire pit such that they are treated by the hot decomposing matter in the fire pit. A heat exchanger and roaster are operably connected to the exhaust of the afterburn chamber. An input mechanism for controlling input of chopped waste materials is connected to the preheat chamber.