Experiments with an inshot burner used in residential natural gas furnaces are School of Aerospace and presented. The concentrations of NOx, NO, and CO in the combustion products of Mechanical Engineering, partially aerated natural gas flames were measured in a laboratory combustion chamber When the conventional circular venturi inlet of the inshot burner was replaced by elliptic venturi inlets, an increase of up to 30 percent in the primary-air entrainment and a decrease of lip to 20 percent in the NOx emission index were observed. Temperature field measurements in the flames were in conformity with the emission index measurements.