No it doesn't lol, they are meant to over come the restriction in the long runs, I'm talking about the wheel type as well and not the propellor type, that may be where the confusion is. High pressure drop is the issue and they are designed to over come that, elbows and such. The cfm rating has nothing to do with the air coming before it from the furnace, how can they rate the cfm's fepending on the air upstream, when it could be 5 cfm or a 100 cfm? They are rated at the amount of air they can actually move but yup it decreases as that restriction increases, same with all fans. Again it depends on the design, prop types are shit, wheel types are made for duct applications.