You reach a metal door and you can hear evil cackling from the other end. Iceman can obviously freeze his way in, but that might give it away. Plus, Hama's a waterbender. There IS an air vent but you're not sure where it goes or how big it is. What do you do now?
We've got no way of knowing if the air vent goes anywhere useful, and given if I was a villain I'd have all air vents in my secret lair booby trapped I'd rather not risk it. Set Iceman to work on freezing the hinges so a solid kick will break the door off.