I would like to install a window type A/C unit in a wood framed wall with a
brick veneer.
The unit will only need to cool one 14'x14' room, so I am hoping small
unit/opening will suffice.
The opening will be on the first floor of a two story structure, so there is
a lot of brick above with no other openings.
The brick and structure are in good condition.

How big (wide?) can the opening be before I have to install a lentil? Could
a wood header/stud/sill frame inside the new opening suffice?

Thanks for any ideas or suggestions.