There needs to be some air exchange, but that can be achieved as easily as opening the cage door every few days. The problem most keepers run into with ventilation is with screen tops. What you have in that situation is heated air escaping through the top, and that heated air takes moisture with it. This can result in a dangerously dry environment, especially if high-wattage bulbs are used.

It doesn't seem like you are using a screen (or open) top, but that is what people on forums are usually harping about when it comes to the topic of ventilation.