i have an antec case which has the option for three fans,
Fan1 = back of case, 120 x 120mm
Fan2 = side panel, 80 x 80mm
Fan3 = front, 80 x 80mm
At present a have Fan1 extracting, Fan2 not installed, Fan3 intake. However it's very noisy and i want to look at changing the fans, also...