the carbon filter has 8'' 720 cfm and the light 8'' 470cfm booster fan. if you look at the first pic the 8'' sheetmetel in the corner has a filter in it and it pulls air from under the house for the light. the other 2 6'' are for attic air or cooler air from under the house i thought i can pull from the floor during the summer and the attic in the winter everything has inline filters.