Duct losses determination

Hi,

I have the duct sized with equal friction method, and now I need to determine the losses.
I'm not sure about the calculation, how ever when I reffered the Carrier handbook, it says to determine the equivlent length and to multiply it with the friction rate (which is assumed constant through the entire duct length). However, with another calcultion, the friction rate is determined for the varying sizes of the duct. I am confused between the two.
Any suggestion?

I appreciate an example in FPS unit!

Thanks
Nevin.

There are a few free online Ductolators that will do the job for you

http://electrical-engineering-portal...-ductulator-09

http://www.docstoc.com/docs/87376410...idth-or-Height

http://www.lorencook.com/downloads.asp

http://efficientcomfort.net/Calculators.html

For a simple to understand guide Google "Woods Guide to Fan Engineering" you can download the book as a PDF file and print it if you prefer.