I am curious about the placement of the various components in a fairly small grow box. I know the exhaust fan should be on top because heat rises; but should it be in the center of the ceiling, or can it be in one of the walls as long as it is up high? Same question with the circulation fan; can it be placed anywhere as long as it is even with the light? Finally, lights, are there more preferable places to put them, or is right in the middle of the ceiling good enough?
Doesn't matter where the extraction fan is placed as long as it's sucking the air from the top area of the box. yes it can be a wall or ceiling. the circulation fan can be placed anywhere in the space as long as it's blowing air across the grow. It's better to be level with the canopy or slightly under it. Lights should be directly over the plants, so usually the middle is prefered.
light should be above the light (to cool the light). and possibly have a circulation fan and possibly point it / add another to cool the bulb(s)