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qnzkrew 12-28-2007 11:26 AM

main line to feed attic
what i need to do is feed my attic with atleast 700 cfm so i can feed 4 rooms in the second floor. i will be coming of one side of the plenum with rectangular duct and goin throught the second floor and sexond floor into attic. i think the size is 16 * 8 or 20 * 8. well my main questuin is once i run the rectangular duct to the attic do i need to put another plenum in the attic in which to connect the round ducts that will be feeding the 4 rooms with heat. or do i just use a 14 or 16 round duct and den branch off the round duct in the ceiling

hvac122 12-28-2007 02:59 PM

You need to do a manual D on the system to figure out what sizes you need. This would take into account how many turns, static pressure desired, velocity etc. There is no good rule of thumb to get it right.

qnzkrew 12-28-2007 03:42 PM

my main question is, do you go from rectangular duct into another plenum in the attic of you would just connect directly to the duct that goes to the second floor. i am really sorry guys if i am annoying anobody with these questions is that i just want to make i ask as many questions as i can . i just like to be well informed before i tackle anything. i am aware i would need to do a manual d to size the ducts correctly as i already did a muanul j for my heat and loss of my whole house. i just want to know how the transition of connections go . thanks again

hvac122 12-28-2007 03:54 PM

Either square or round as long as its sized properly. We would run a trunk line down the attic and branch to each room with dampers on the takeoffs.

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