A glass forming apparatus includes a glass delivery vessel, a forming body with a forming body inlet and a downcomer (48) between the glass delivery vessel and the forming body. The downcomer includes a downcomer tube (100) with an inlet end (110) for receiving molten glass from the glass delivery vessel and an outlet end (109) for discharging molten glass to the forming body inlet. An upper heating zone (110) and a lower heating zone (150) positioned downstream from the upper heating zone (110) encircle the downcomer tube and a lower controlled atmosphere enclosure (155) is positioned around and sealed to the downcomer tube (100) in the lower heating zone (150). The lower controlled atmosphere enclosure (155) includes at least one heating element (156) for heating molten glass flowing through the downcomer tube within the forming body inlet.