Duct CFMs for home A/C

Guest,

I do not think that your question can be easily, accurately, answered due to some needed information.

That is, you need to take into consideration the static pressure of the entire length of duct, including taking into account all friction factors and losses due to discharge grilles/caps, elbows, turns, etc. in the ductwork, as well as the ductwork material itself. (Flexible ductwork has a significant friction loss, adding 25 to 50% onto the "Equivalent Duct Length" (EDL)

There are standard values for different duct components that can be referenced.

However, if you want a short answer, given a straight 60 foot run of 4" smooth metal ductwork, you could reasonably deliver between 50 and 90 CFM, dependent of course upon the power of your blower fan.

Thanks JMAN, all they wanted was a ballpark figure. That'll do it!

keep in mind any velocity above 10m/sec will be noisy

A ductilator calculates pressure drop given duct size, shape and airflow.

For a 4" line I would not push more than 60 cfm through it. That's about 700 fpm with a pressure drop of about 1/4" per 100 feet of straight galvanized round duct. If it is flexible duct, the pressure drop will be more, as high as 1/2" per 100 feet. The external static pressure (ESP) available from most home type furnaces (especially if it has a cooling coil associated with it) is not very high, less than 1".