Air Conditioning - designing heating and cooling plan for soon-to-be finished basement

I have right at 400 sq ft that I plan to finish in my downstairs section of my house. I plan to do a zoned system and am having trouble calculating exatly what my needs are.

I have one room that makes up 300 sq ft and another room that makes up the remaining 100 sq ft.

I am guessing that I need to run 12" duct from the plenum and 8" for my supplys.

There is also a bathroom that I plan to run a 6" line into.

And finally 8" return lines 1 from the large room and 1 from the smaller room.

Can anyone confirm if my plan sounds reasonable? Or by all means please feel free to recommend changes.

Thanks

Id run two 6"pipe off the trunk line to the outside wall put a 90o 2 1/4"X12" boot 12 " in off the wall blowing down. just one for the other room and a 5" for the bath down there. A cold air return down low in them or just one near the furnace and cut the bottom of any doors off 2".

ED ;)

i am assuming your reply agrees with my thoughts of using a 12" off the plenum?

Thanks for your comments!

:confused: There we take all takes off the top of the trunk line :confused:

ED ;)

Like Ed says but make sure you don't put a return in the bathroom.