A stack is provided for combustion of low pressure hydrocarbon vapors from various equipment, the combustion being discrete from periodic flaring of high pressure vapors from a top of the stack. A primary burner is positioned adjacent a base of the stack and a flare is positioned in the stack's bore adjacent a top thereof. Combustion air is naturally aspirated through the stack through inlets in the stack below the primary burners, providing both primary air and secondary air for the primary burners and first combustion air for the flare. The flare aspirates further combustion air from about the top of the stack. The combustion air optimizes clean burning at the primary burner and for reducing smoke production from the flare. A controller provides an auto re-light igniters at the primary burner and a continuous igniter at the flare.