HVAC takeoff advice needed

[Giantsean]

Hi All,

At long last I am fixing to install two additional return registers to my system which has been struggling to breathe and move air for about eight years. The return trunk is 8" H x 16" W. As I have lengths of 6" and 7" flex leftover from the install, I want to put them to use. The 6" run is not a concern as I have space, but the 7" takeoff is raising some questions. You can see from the pics the joist bay from which the flex will drop down. Originally I had hoped to take a 7" round starting collar straight into the 8" side, but as you can see there is a lot going on in this area.

Assuming a 7" starting collar is not already too big for an 8" duct, I might have to move the condensate line up a bit (above the wires and tighter to the joists). I could also attach it (or a square takeoff) to the bottom though it's not ideal. The top is not accessible at all.

Last option is I could just go 6" on this one though I really want to maximize the airflow. From my understanding there's no such thing as too much return air.

Thanks for any advice on how to best do this!

 

[Fitter30]

8 x 16 = 128 sq in
Minimum 144 sq in per ton
What size filter?
What tonage is the ac?

 

[Sponsor]

 

[Giantsean]

It is a 2-ton Trane TAM7. Filter is 16" x 20". the main trunk return duct is the 8x16 for it's entire length (around 40'). I should add there are already four return ducts total in the system with following register box sizes:
6 x 10
6 x 12
4 x 14
4 x 14
(all are 6" or 7" flex except for one 5x14 which is directly over and connected to the trunk duct)

I am looking to add two more return registers both 6x12 one using 6" and one 7" flex. Besides the excessive suction on the return side, I am trying to get better air circulation in the kitchen and breezeway, both of which are next to each other and neither have a return. The kitchen has a dining area w/ a space far enough away from the cooking areas (>10ft) so it should not be an issue - checked this w/ the bldg dept.

Thanks!

 

[Fitter30]

8" should be enough for 7" using a collar. Duct is probably put together with a pittsburgh seam mating the corners. Hole cutter works very well if there's clearance.

https://www.amazon.com/Adjustable-Stainless-Klein-Tools-89552/dp/B07DLT79N8/ref=asc_df_B07DLT79N8/?tag=hyprod-20&linkCode=df0&hvadid=693614504112&hvpos=&hvnetw=g&hvrand=8167879000043218268&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9022830&hvtargid=pla-570094410925&mcid=d8b701f5c17a3fc6b541764a5a0b68e5&gad_source=1&th=1

Pittsburgh Seam: Small vs Large – Conklin Metal Industries

www.conklinmetal.com

 

[Giantsean]

Thanks! As far as airflow, no issues running a return straight into the trunk duct at a 90? (Vs more of the "wye" or 45 bend.. not sure what the term is for ducts...)