Venting exhaust out a window a/c unit

So the warm months are starting to creep back up on us, and its time for a new a/c unit. Do the extraction fans on window units have to power to suck out the hot air from my hood or should I think about other means? I will prob be putting 4" flexible ducting right up to the grate on the front where I assume it sucks air from the room. Any help would be muy appreciated.