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Single return box goes to two rooms, no privacy

1933 Views 21 Replies 7 Participants Last post by  zx7king

In our home we have a single return box that has a filter on one side to the front hall and on the other side to the master bedroom. So basically if the filters are clean you can almost see through to the bedroom and certainly can hear. Not a lot of privacy when you consider the other side is the front hall and living room area.

What is the best way short of separating them into two returns? Is there a way to "divide" the current box?

Any advice is appreciated.

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LOL... get a motel room??? LOL

seriously, I suspect that you could insert some sort of Divider that would allow the air flow to still get to the ac system, yet block the "view". If you use a sound absorbant material like ductboard (which I hate and suggest that you coat all exposed fiberglass surfaces to reduce fiberglass particals in your air stream!!) you might lower the sound transfer.

if it was me I would line the entire inside of the box with sound absorbent material and make a dividor also!!!! besure you can clean the material if you need to!!!

or maybe go with a media type filter. The filter material is about 4 inches thick and should help to reduce sound transfer also!!!
hehe.. thanks for the reply. i knew i was going to get one like that :).

Can you get ductboard at the big box stores?
I know it would protrude into the room slightly but you might consider installing a cover in the bedroom side like a flat board with feet that mount to the wall thus leaving an air gap all the way around OR at least on two sides to allow correct air flow. e.g., a box with only 2 sides mounted around the opening.OR .if it could be mounted with just feet and open all around it wouldn't have to extend as far into the room..I think it might be more secure and prevent materials coming loose and returning into fan compartment. Just a thought. Whatever you do, make sure it is anchored securely.
Depends on how it is set up, do you have access to the duct work below?
It might be possible to cut into the duct and add another elbow on the end, that elbow so you can reach outside the bedroom wall and put return in the bedroom floor.
Now you can close up the drywall on the bedroom wall.
Would need to see it to suggest a better way, but the idea above may give you a better idea.

Also might try some of the better allergy filters, are thicker and tighter woven, would help some.
Post pic of box, and how its ducted.
A pillow over my wife's head works well.....'s a good question.....

The problem with more filters or material is that you restrict the flow of air.

You may have to cut a hole in the ceiling and run a duct up and over....

I'm still trying to figure out what I'm going to do for my master bedroom.....I don't want my kids to think I'm spanking their mom...
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Put a full sized divider in just to the left of the flex duct..

Then cut the floor out bigger, and run a second flex up to catch the other room.
Wow! take the picture back .... just brings more questions :laughing:

I assumed was a shared wall.
You have that much space between the hallway and bedroom wall, or is that in a basement?
Just not understanding that photo, looks like wasted space to me.

But could just cut out the middle of that duct, put in a Y and run separate returns off the Y
Yes that is under my stairs that is not in the basement and it is wasted space in fact the reason you can see it is because I broke apart a small coat closet which I'm making bigger in fact I'd rather disassemble that entire return and push it forward in that picture about 4 feet towards the bottom of the stairwell what do you think about that idea?
well, a picture sure did help!!! The flex duct looks small and I would bet you money that the static pressure is fairly high, given the wrinkled condition of the ouside jacket. I could be wrong, the inner duct work might be pulled tight and installed correctly, but again, I would bet not.

so if it was mine.... I would remove the flex and install 2 sheet metal return ducts back to the air handler. I would then install two filter racks and grills, one for each area. this way they would be separate. This will also help the system breath better. And since you have the space, I would put really deep filter racks in and then run 4 inch media filters. With media filters you get better, less restrictive, filtration of the air, plus you normally change the filter less often.

bottom line is that I would split that T system you have today and run two new, "big ol" return ducts, with two new filters.

Then you can, get loud as you want to...
Thanks for the replies !!


Actually that flex duct is 16" internal diameter. Not being an HVAC expert not sure if that is considered "small" or not. Is an option to go under the house and install a "Y" onto that flex and then run two up from the crawl to the new location? If so, i couldnt find any parts at the big box stores to do that or i was just not identifying them correctly. For instance i saw no "Y" or "T" for flex that big.

You are going to have to go to a real hvac supply company for a "Y" that big. additionally, since you are working on the flex, be sure you read up on how to correctly use it. The highlights are that you must pull it tight, have no sags or bends. It must be supported. Where the flex attaches to any metal, you must install screws that capture and hold the inner wire (i use self taping screws with small washers). Then you must mastic or tape to seal the liner. I use mastic and tape both!!. I also use the really big zipties as backup. the bottom line is that flex is ok if its pulled tight with no bends etc and all the above is done to secure the sheet metal to flex connection.

I would consider removing all the return flex if you can and install metal. Reason is that you cant really clean flex.

and while your at it, consider new filter racks that hold the big 4 inch media filters. You will be amazed at how well they clean the air, how long they last and how little effect they have on the systems static pressure (air resistance)

check out this site for a start
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Thanks again for the replies. Here is my latest plan. If you look at the picture in the thread...

I would like to pull that 16 " duct back down through the floor, extend it and have it come up further under the stairs to service the hallway and rest of the downstairs on the left.

Then I am going to run a separate return for the bedroom on the right all the way back to the air handler.

My latest question is :) .. the second return is only servicing the master bedroom. Since i am purely adding this.. i.e. not downsizing what is there already, i was hoping to get away with something a lot smaller.. 8" flex duct maybe? Is that okay?

not an expert here... but it looks like a 16 inch flex will allow 975 cfm at .1 static pressure and it looks like an 8 inch flex will allow about 175 cfm at .1 static pressure. so by adding the 8 inch flex return to to the bedroom, you should be decreasing the static pressure in your system.
but since you are taking out a return grill on the 16 inch return, you might end up with some pretty fast air flow at the grill, which might make some noise. i dont know where your filter is,, but if its in the grill, you might be jumping up the fpm on the 16 inch return filter. if the filter is at the air handler, you should be fine.
thanks again. yes, the filters will be in both grills. So if the noise is not an issue (in hallway) is this okay for my system to reduce the static pressure as described?
How many supplies in bedroom, and what size are they,.
two and they are the standard small floor ones.. ~11x4 .. there is also one in the bathroom attached. Thanks.
Why not install a thin solid divider (such as thin plywood) vertically directly over the middle of the round duct below?

Cut a hole in the existing rectangular duct, directly above the existing round duct, to add more ductwork to extend the return ducting to other locations as desired.
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