A Round Main Duct Question

[radstorm]

What size round duct could feed the following branches: 7 x 6" and 2 x 4" All branching off from the main round duct. ?

It would look sort of like this:

http://composer-world.com/images/roundple.jpg

I realize this is not the usual beaten path method, but apparently it can be done. So I am just wondering as in my case round duct is easier to work with and less costly.

[HayZee518]

I would have to guess a ten inch round. a trunk line off a plenum is usually a 12X24 given the cfm of the blower motor.

[radstorm]

Thanks HayZee, that was my guess also. I figured at least that or maybe 12"

[paul52446m]

A Round Main Duct Question

What size round duct could feed the following branches: 7 x 6" and 2 x 4" All branching off from the main round duct. ?

It would look sort of like this:

http://composer-world.com/images/roundple.jpg

I realize this is not the usual beaten path method, but apparently it can be done. So I am just wondering as in my case round duct is easier to work with and less costly.

We usually lay out hot air ducts to a .10 static pressure. 6"rd will carry 110 CFM of air. 4" will carry about 40 CFM. So you have about 850 CFM. that can come out your branch runs. A 10" is way to small.
10" at .10 static pressure would carry about 410 CFM.
12" """""""""""""""""""""""""""""""""""""""""""""""""" """690 CFM.
14" """""""""""""""""""""""""""""""""""""""""""""""""" """"1000 CFM.
Now if you are using flex rd. duct the corrugation restrict air flow so i would go with the 14". Paul