I am currently working on a home addition of just under 1200 sq ft finished. I had a HVAC person size the air and heat. I have about a 65000 btuh high efficiency gas furnace and a 2 1/2 ton air conditioner at 13 seer. I am using a duct calculator to set my duct sizes. I am trying to use standard size duct to avoid the cost of shop labor to make custom ducts. So I am trying to work backwords from the duct sizes to the CFM and Static pressure. I did HVAC for about twenty some years and did a little installation of HVAC. I need some help sorting out how to use the duct calculator.
For metal pipe duct or rectangular, set the friction scale at .10
for flex duct set it at .06 for supply and .09 for return. Then just line up your desired cfm and it will tell you the proper duct size.
Thanks for the input. I have worked on this for several days and could not get a good answer. I even went to the local Junior college and bought a book on duct sizing and still had problems getting all the data.