Every different size of filter provides a different resistance to each different size and style of fan you put on it, a filter at the maximum exhaust CFM rating has approximately 0.7 wg. pressure drop. All fans will have a lower CFM at a higher pressure. Can-Fans® and Max-Fans™ are highly efficient and lose the least amount of CFM when put under a resistance. Can-Fans® will only lose 15%–20% of their air flow through a fi lter. Max-Fans™ only lose 7%–14% of their CFM All other fans lose up to 60% of their CFM. For example at .5″ wg: The 10″ Max-Fan™ goes from 1019 CFM to 885 CFM. The 12″ Max-Fan™ would go from 1708 CFM to 1595 CFM.”