I was in the process of having a humidifier installed on my Heil 5 ton Heat pump when the technician informed me that the supply line on my unit was too small. He indicated that based on his duct calculator, I would require a 18 inch round duct to provide 2000 CFM rather than the 14 inch that was installed. He also said the He indicated that he used a friction ratio of .1 in his calculation. I don't know what the friction ratio means. I called the original installer and he indicated that since the unit was in service for 5 years that it was probably ok. The original installer sent out a new tecnician and he indicated he uses a friction ratio of .5 in his calculations.
I don't know who to beleive or how to get to the bottom of this delima. I called the manufacture and they indicated that I need 2000 CFM but they said that they could not provide duct size information. What is the correct friction ratio and how does it affect the duct size? Any help or suggestions woule be greatly appreciated.