One embodiment is directed to an oven for heating fibers. The oven comprises a plurality of walls forming a chamber and a supply structure disposed within the chamber between first and second ends of the chamber. The supply structure is in communication with a first heating system and is configured to direct heated gas from the first heating system into a first portion of the chamber. The supply structure is in communication with a second heating system and is configured to direct heated gas from the second heating system into a second portion of the chamber.