There are two distinctive styles of Hoods designed to remove grease laden vapors from a commercial kitchen:
Exhaust Only. This style of hood is intended to have a Make Up Air solution in another part of the room, i.e. opposing wall diffuser, or ceiling diffuser.
Built-In Make Up Air. Also known as Internally Distributed Make Up Air. This style of hood is designed to eliminate the need for Tempered (or Climate Controlled) Make Up Air, as it has a supply plenum built in to the front of the hood directing the Make-Up Air gently toward the cooking equipment and back toward the filters.