A three dimensional thermo-fluid mathematical model of the load tank of a continuous natural gas glass furnace has been developed. The main objective of this work is twofold: the successful coupling of this model and an existing combustion gas model, which simulates the combustion process; and the study of the variation of several furnace operating conditions and their impact in the overall furnace performance and glass thermal behavior. This model provides important information about the heat transfer characteristics of a commercial type glass and how these are affected by the variation of the radiative properties of the load (glass) surface and refractory surfaces in the combustion space, as well as by the incoming air temperature to the combustion chamber. This paper includes the results of three-dimensional velocity and temperature profiles of the glass flowing through the furnace. In addition, the results of a parametric study on the glass surface emissivity, refractory emissivity and preheat air temperature are included.