Tom - There is NO limit on the number or size of ducts in the air dam. The only limit that applies is the number of holes you can cut in the front valance, which is basically one hole per side for a 3 inch diameter duct. As long as you don't cut more than one 3" hole in the valance, you can run as many ducts, and as big as you want, if you can figure out where you can run them (other than through the valance).