Enclosing a room that has a central air return

Sorry for the length, I am looking for feedbacks and opinions here.

I want to enclose a 12x12 room (with two large open walls now) currently open to the rest of the house, and convert it to a den. It is a very easy task from a framing perspective. 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 with 2 15 inchh ducts.) 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 and a 30 inch door 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 frame for 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.

Have you considered a decorative louvered door?

Welcome Vistav:
Craig's louver door is a good choice. Even if it is a solid door at the top and louvered at the bottom. How ever you go at it; the number of square inches of the new openings should equal or excede the square inches of the current grille. The 20 X 20 grille has 400 sq. in. The double door will give you 48 sq. in. and the other door will give you another 30 sq in. leaving you needing 322 sq. in. to make up. A back to back High wall grille 30 X 12 would make it up.
Just my ramblings and thoughts on the subject.
Glenn

glennjanie said:

Welcome Vistav:
Craig's louver door is a good choice. Even if it is a solid door at the top and louvered at the bottom. How ever you go at it; the number of square inches of the new openings should equal or excede the square inches of the current grille. The 20 X 20 grille has 400 sq. in. The double door will give you 48 sq. in. and the other door will give you another 30 sq in. leaving you needing 322 sq. in. to make up. A back to back High wall grille 30 X 12 would make it up.
Just my ramblings and thoughts on the subject.
Glenn

Click to expand...

Thanks for the replies!

I won't consider a louvered door partly because of aesthetics, but mostly because it does not provide sound and light prevention I need.

I am curious that the calculation is as simple as "make sure you have openings equal to the surfce area of the current return air intake." If that is the case, my task is easy. I was inclined to think the calculation as not so straight forward because of the impedence of thinks like the grill vents and obstructed air flows.

Lastly, any negatives to mounting the back to back grills at a verical offset to allow for more light and sound privacy?

Hello Vistav:
The square inch calculations should equal or EXCEDE the size of the present grille.
You could try one back to back with the offset situation and another could be added later if it doesn't work out. If the air comming into the room is noisy or sounds restricted then it is not sufficient size.
Glenn

glennjanie said:

Hello Vistav:
The square inch calculations should equal or EXCEDE the size of the present grille.
You could try one back to back with the offset situation and another could be added later if it doesn't work out. If the air comming into the room is noisy or sounds restricted then it is not sufficient size.
Glenn

Click to expand...

Thanks. I am going to give this a shot. Along with the planned door undercuts, I am going to install two offset back to back grilles. If needed, I will add a third (or heaven forbid fourth) set.