Exaust vents on central heating and air.

[Therrion]

I am building a grow room and I split the room into 2 halves. It will be air tight. The only question I have is my AC exhaust vents are on top of the ceiling of the flowering room. Will the smell back fill into the rest of the house when no air is coming trough them? If so how could I remedy this without using a portable ac and blocking off the vents or is that even possible. It is the last stop for the ventilation system and about 15 to 20 ft until the next exhaust in another room. I don't have much hvac experience. Just so you know I am venting the heat to the outside via a carbon filter.