Abstract: A venturi nozzle for a gas combustor includes an orificed gas nozzle, a venturi tube and one or more support members. The orificed gas nozzle has a longitudinal axis, an inlet and an outlet. The venturi tube is aligned with the longitudinal axis and has an entrance proximate to the outlet of the orificed gas nozzle and an exit. The support member(s) are attached between the orificed gas nozzle and the venturi tube to create a gap between the venturi tube and the orificed gas nozzle. In some embodiments, two or more venturi nozzles can be combined together in various configurations into a nozzle assembly or multi-nozzle gas combustor and attached, mounted or disposed within a stack, chimney or vented enclosure. The wall(s) of the stack, chimney or vented enclosure may include one or more openings, cut outs or vents to provide primary and secondary air to the venturi nozzles.