Help Relocating Supply Plenum in Remodel

[Europe72dead]

Hello,


BACKSTORY-


I’m in the middle of renovating a kitchen and in doing so need to relocate my primary supply plenum that services the entire first floor. It was previously 10” tall duct board and located in a drop ceiling over a 1/2 bath.


GOAL-


I am relocating the 1/2 bath and in doing so I want to gain some ceiling height. I plan to make the new metal plenum only 5” tall and make up for the necessary CFM by expanding longer and wider since the new bathroom will have a larger footprint.


The current plenum is duct board, the inner dimensions are 34”x19”x8” totaling 5,168 CFM.


SOLUTION-


I plan to make the new plenum something like 40”x26”x5” totaling 5,200 CFM. Ducts will attach in similar locations to where they were on the original plenum. Duct work will be kept to a minimum in the new setup since the plenum will be very close to each register. The whole trunk will be moving to the left a good foot as well. I’m expecting roughly 1 or 1.5’ of duct work between each collar and register.


QUESTIONS-


-Do you see any major issues with this change?


-Is the hard 90 from the trunk to the top of the plenum acceptable or should I really come in from the side with a 90 degree shortway trunk elbow? This would require me to push the entire plenum over 6-10”.


Here are some photos of existing and new ideas. Thanks!!!

 

[Fitter30]

Come in the end bottom of the drop make a turning vane out of round pipe. Expand the duct to the full 26". That 5" depth will increase the duct static pressure . Possible more noise less air flow

 

[Sponsor]

 

[Europe72dead]

Let me draw this out and post. I’m somewhat following. I assume the 90 degree shortway elbow would need to be a custom piece that attaches to the 10”x21” trunk and then expands to a 5”x26” since it will now attach to the side of the plenum? (Where I have the 6”start collar which will now need to move). Is this correct?

Also, I’d love some clarification on where exactly these turning vanes would be if there is a rounded 90 entering the side of the plenum as opposed to the top.

Lastly, it would be easiest to have the trunk connect to the top of the plenum, is there no way to achieve this efficiently?

 

[Fitter30]

You have 210 square inches on the drop, 26x5 = 130 sq.in. Put the vane in the heel of the fitting to help turn the air instead of a square corner.

 

[Europe72dead]

I am now understanding that it isn’t advisable to drop the trunk directly into the plenum. Is it normal practice to put vanes inside the plenum to achieve this?

If going into the side of the plenum is my best bet I will have to source something like the attached elbow that will drop down from the trunk and insert into the plenum.

if I take this route, will I have trouble with the one 6” duct that will be right next to it?

Thanks

 

[Fitter30]

The reason for the end of plenum the air wouldn't slamming into the bottom 4" away.