Dont understand why the 2 fans ,ya only need 1 fan ,follow delvite Post ( drawing ) Not the picture , although he has the theory of exhausting correct , each time you bend the flexable duct to a 90deg turn its like adding 40 feet of straight duct to your application ,therefore hindering the air flow and effecting the fans true capability. So when you look at his design witch in theroy is correct .but he has 3 90deg turns (elbows) witch = a extra 120ft the air has to run ,Ive saud this time and time again here ,you guys spend good money on exhaust and buy top of the line fans and then duct them incorrectly therefore cutting the capability of the fans designed potential by 30% to 50%. ,Air is moved by Static pressure , not like plumbing water PSI. anotherwords you cant hook up duct work like you would plumbing without suffering great effect on air movement.