I've never used a carbon filter so I don't really know about that, but I've always heard that you want to push hood air to avoid the smell leaking? Pushing the hood air causes positive pressure in the hood which won't result in a leak, but pulling the hood air would cause negative pressure and with some hoods you run the risk of pulling air from your grow into the hook.
If it's a normal exhaust for the room itself then pulling the air is definitely a huge fail, but doing so with hoods can cause potential smell leaks.