A device for gasifying biomass waste has two each of primary chambers, fume transfer vents, mixing chambers which accept fumes from the primary chamber, afterburner chambers in fluid communication with the mixing chambers, and an exhaust duct. Each secondary burner produces an initial heating flame within a vertical portion of the respective afterburner chamber, and secondary chambers are in fluid communication with the afterburner chambers. Heated gases from the afterburner chambers cause heating of the secondary chambers. A portion of each primary chamber has a heat conductive floor superimposed over the respective secondary chamber, and the partition between the primary chambers is heat conductive, so that conductive and convective heating of the primary chambers occurs.