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Old 01-28-2008, 09:44 AM   #1
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Enclosing a room that contains a central return


Apologies in advance for length ....

I want to enclose a 12x12 room that is currently open to the rest of the house, and convert it to a den. The problem is, one of the (2) central return air vents/ducts for this zone is located in this room. The Return grill in this room is 20x20, with I am guessing at least a 15 inch round duct. There is a filter at the return grill. (The other filtered return located in another common room, is larger, at least 20x30.) They feed a 5 ton unit.

Current design makes extending that return to outside the newly enclosed room problematic. My solution is to install some pass through grilles in the new (2x4) wall I am erecting.

My question is, how do I compute the total pass through grills I will need to add to the new wall, if I assume that there will be a one inch undercut beneath a set of (4 foot?) double doors as well. Will it even work to add these grilles, which I plan on offsetting to help with noise and light, in a 2 x 4 wall, or do I need to go to a 2x6 fpor more pass through space?

Aesthetically, I can not put in 5 or 6 smaller grilles in the new walls, but I can probably get away with 3.

Hope this was clear, help is appreciated.


Last edited by VistaV; 01-28-2008 at 10:17 AM.
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Old 01-28-2008, 12:33 PM   #2
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Enclosing a room that contains a central return


Is there room above the door?

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Old 01-28-2008, 12:45 PM   #3
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Enclosing a room that contains a central return


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Is there room above the door?

Hard to explain the scenario, but ....

Yes, probably will be at least 8 inches of rough in space between the new header and the existing dropped down glue lam beam which the partition will be built under. Probably closer to 12 in fact. I was considering putting one of the grilles I mentioned above the door. In fact, there might be space ABOVE the current beam which is where it would look best (because it would line up with an ezisting register in that room.

At issue is not really WHERE the pass throughs go. There are some aesthetic issues that may dictate that. I just need to make sure I have enough of them to let enough air in to the room for the return.
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Old 01-28-2008, 05:48 PM   #4
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Enclosing a room that contains a central return


Can you put the return in the ceiling outside of the enclosed space?
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Old 01-28-2008, 06:03 PM   #5
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Enclosing a room that contains a central return


how about 2-10" X 20" long rectangular grills just above the molding in the new room on each side of the new doors into the space...or one long grill in the far corner of the new wall and out of the way possibly opposite or nearest the exsisting 20x20.if the door will be open when the room is unoccuppied there is your natural return....live dangerously build the wall and see how much that exsisting is sucking air thru the door when it is closed
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Old 01-28-2008, 06:22 PM   #6
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Enclosing a room that contains a central return


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Can you put the return in the ceiling outside of the enclosed space?
Hmmm, No, not really. The 20x20 return is actually currently in the wall, at the top. It woould be difficult to move, period, and IMPOSSIBLE to put in the ceiling. (flat roof).

I could, strictly speaking, add 12 feet of duct, drop the ceiling in all of the current room by 18+ inches, and move the return out in to the common area. This is SIGNIFICANT, in fact prohibitive work, when compared with what I hope is a feasible alternative.
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Old 01-28-2008, 06:32 PM   #7
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Enclosing a room that contains a central return


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how about 2-10" X 20" long rectangular grills just above the molding in the new room on each side of the new doors into the space...or one long grill in the far corner of the new wall and out of the way possibly opposite or nearest the exsisting 20x20....
Sure, I can probably put 2 10" x 20" grills in there, or even 3 of them if I [put one on adiferent wall. What I really need to know is if this is enough pass through space to meet the demands of the return, which leads to ....
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.....if the door will be open when the room is unoccuppied there is your natural return....live dangerously build the wall and see how much that exsisting is sucking air thru the door when it is closed
Well, I probably will just build it with two grills, and give it a try like you said. There is the undercut of the doors as well. I can always punch another one (two?) if I have to. Although the doors will be open "often", they will be closed for long periods, and it should be tested and engineered under that assumption.

Back to one of my original questions, does anyone have opinions on whether offsetting the grills by 8 inches on each side of a 2x4 wall will allow enough air flow through such a narrow space, while still allowing some light and noise prevention?
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Old 02-16-2011, 10:35 AM   #8
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Enclosing a room that contains a central return


I too have enclosed my dining room which has the central return located in that room. The central return is 22x22. I have one door (8x3 foot) with small space below door of about one inch. I will be placing 2 vents of 24x14 in the newly constructed wall. Will this be sufficient for air flow to the air handler or will it be causing the ac unit to stress and cause the coils to freeze. Also, is placement of the vents important as the central return vent is located near the floor as the vents will be about 9 to feet up on the one wall. Should i space the 2 vents apart or does it matter.

Thanks
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Old 02-16-2011, 12:51 PM   #9
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Enclosing a room that contains a central return


I can only offer a guess based on my experience.

I think the scenario you describe will be "close" and is worth a shot.

If this is the only return air for that system, it is much higher risk. If there is another return air for the system, I would very much think you will be ok.
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Old 02-16-2011, 01:08 PM   #10
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Enclosing a room that contains a central return


Unfortunately, it is the only return. What do you mean by high risk?
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Old 02-16-2011, 01:24 PM   #11
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Enclosing a room that contains a central return


[quote=VistaV;92830] The problem is, one of the (2) central return air vents/ducts for this zone is located in this room. The Return grill in this room is 20x20, with I am guessing at least a 15 inch round duct.


I assume that it is not as simple as the return being on an interior wall that you can simply open up the other side and put the grill there and then drywall the existing vent??

rod
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Old 02-16-2011, 01:57 PM   #12
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Enclosing a room that contains a central return


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I assume that it is not as simple as the return being on an interior wall that you can simply open up the other side and put the grill there and then drywall the existing vent??

rod
As the OP, I did my project three years ago.... (but no, it was an 'exterior' read, garage facing wall)

My project worked great. I have a double door with undercut, and put two new ~10x20 pass thrus in. Since this is one of two returns on the system, I have had no issues.
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Old 02-16-2011, 02:00 PM   #13
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Enclosing a room that contains a central return


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Unfortunately, it is the only return. What do you mean by high risk?
"risk" of not being enough pass through surface.

If it were me, I'd try it with your two vents assumign you do not have spots for three.

Worst case you can leave the door open while you figure out where to add another vent .......
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Old 02-16-2011, 02:15 PM   #14
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Enclosing a room that contains a central return


Sounds good. Off to Home depot to purchase more vents. I will post how it went once I have placed the new vent in the wall.

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