It is true that all reptiles need regulated heat/humidity, but iguanas are especially sensitive to environment, and improper heat/environment is the number one cause of death in iguanas.
I have had snakes as pets for more than two decades now. Our last being a python named "Monty". Will try to dig up a picture. My snakes have ONLY grown large when moved into a larger tank. Once they have reached capacity for the size of the tank, they slow down on their eating so that they do not grow beyond the environment. Monty was just over six feet, and by then was in a tank that was as long as the wall.