tempestjhonny
I,d get a blower larger than 270 cfm...im guessing in the rang of 350 cfm cuss . cuss of the length of ducting you.ll lose alot of mass (air movement ). and elbows will slow it further, thats why you need more cfm . some use ordinary home dryer ducting ,which is even worse because of the accordian shape inside . i recommend useing if price an,t a facter is smooth metal heating ducting like you have in your home .secound choice would be the alum, dryer ducting its cheaper and you can bend it ..it,ll strech to 8ft or more .the more sucksion you want, the more airflow you need so the diameter of the ducting is also important too. been there done it.
Id use 4inch ducting for 270-275cfm 5inch for 300-375 or more cfm
hope this helps ..
pete