When sourcing a tempering furnace, you must prioritize heating uniformity and cooling efficiency. Key specs include the heating power (kW), maximum glass size processing capability, and glass thickness range (typically 3mm to 19mm). Ensure the furnace utilizes forced convection technology if you plan to process Low-E glass, as this ensures even heat distribution across coated surfaces. Additionally, verify the SO2 concentration control and the quality of ceramic rollers, which should be high-precision to prevent glass scratches or optical distortion.