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CoryM 07-07-2007 11:37 AM

HVAC rough in
I am in the middle of an addition, all framing and roofing and windows and doors are in, so I have a weather tite enclosure.

( I work in stricly commercial construction, so residetial is a whole new thing for me )
My project is typing new into an old cabin, with limeted access through walls , etc.
I am in a rush to get rough in so I can get the drywall up.
I know the loads for ducting and return area for my spaces. Few questions though before i jump into it.

i will be using 3.25 x 10-12" for vertical supply in between floors, I plan on stubbing off that main with 4" round to feed floor registers in new areas.

I plan on using plenum space in walls for cold air return, likely will have low and high for seasonal. Should I be insulating the cold air return plenum space?

When I encounter an obstruction and cannot contiue square duct vertically, does it make sense to snake through with round or oval then return to square? or have I already increased velocity and continue on in round?

for area over the old section of the house, it will be challenging to get underneath for new floor registers, is it feasible to feed supply air from overhead attic space, drop between walls and supply from low wall registers, or will I loose all my air with that much direction change?


MechanicalDVR 07-07-2007 11:44 AM

You don't have to worry about insulating bay space for return if they are inside walls. I'm not sure why you want to use rectangular pipe instead of oval in the walls. But, yeah you can feed to the attic with a trunk and down from there, it's done all the time.

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