The instructions will tell you the electrical requirements.
Most in-wall units I have done were hard wired to a supplied receptacle in the space under the fire box.
Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
Answers based on the 2008 & 2011 NEC. If you're on the '14 already I feel sorry for you.