A gas burner unit for a cooktop includes a spreader positioned above a top surface of the cooktop to define a gap therebetween and having a plurality of gas outlets. The gas burner unit further includes a venturi in fluid communication with the gas outlets and an orifice holder having a plurality of protrusions defining a plurality of upwardly directed primary air inlets therethrough. The plurality of upwardly directed primary air inlets are in fluid communication with the gap on respective first ends thereof and with the venturi on respective second ends thereof opposite the first ends.