Hi all, 

I’ m redesigning some of my rectangular (H/W=1) duct work in anticipation of a new air handler, and had a quick question regarding a large radius transition on the return side.

Both radius elbows have similar measurements (see attached drawing), but have different outside radiuses which give them a different footprint and area. Because of the way Manual D calculates equivalent length, they both have the same R/W ratio of .714 though and therefore the same EL. 

Being very new to duct design, is one better than the other, perhaps in terms of turbulence? Or, am I overthinking this and there is little to no actual difference between the two?

Thanks for the feedback!