If the makeup air is coming from a static vent in front of the stove, I would think it would have a negative pressure and act like a chimney to the attic. This could suck alot of moisture up there, especially from the kitchen. Maybe there is a flue vent or something to prevent this? Why does the exhaust need so much makeup air that it requires a dedicated source? Is it to prevent blowing 1600cfm of heat outside?

Mike - TurningColorz

Seems like in the winter that may work, but in the summer it's uncooled space, so you're going to be bringing hot air in, no? It's one thing to have cool winter air running over the range, but warm, muggy air probably is not the best.