How should upper and lower oven elements be specified for commercial heating elements?

Upper and lower oven elements need not match in wattage; specify each from browning, base baking and airflow. Measure zone temperature profiles and bake real products at each rack level before ordering. Where multiple baking programs are needed, independent control beats a fixed power ratio. Confirm sheath material, tube diameter, surface loading, voltage, wiring, IP protection, mounting dimensions and sensor position against the actual machine, then accept on measured zone temperature, insulation resistance and leakage current, with revised drawings kept on file.