I am a residential HVAC consultant, selling replacements and add-ons directly to homeowners.

I need some sage advice related to return air design theory / practice to make myself a better consultant.

The training I have been given as it relates to the "Ductulator" is that I should be using a friction / ESP setting of .10 (for both supply and return) However, one of our more seasoned installers recently berated me for being a "wet behind the ears rookie" and then told me I should be using .05 friction when I design or verify the return side of the system.

What say you?

Help me out here-