Originally posted by dash
12" round,10"X11",and 21"X6",all have the same airflow characteristics ,except velociy which will be less in the 10X11 and even less in the 21X6,assuming the same material.Check your ductolator,to verify.

Well everytime I get a customer that wants to save ceiling height by making the ductwork 2 inches deep by 40 inches wide I tell him it just wont let the air flow right being its all surface area and the air wont flow right.



THATS MY STORY AND IM STICKING TO IT......