# Adding return vents to bedrooms



## Dutch2 (Oct 20, 2009)

I'm not sure what information is needed to answer my question, but here's a start...

I have 3 bedrooms and a bonus room upstairs. My house has 2 air conditioners. The one for upstairs has 3 return vents, each with a 14x20 filter and a 12" flexible duct going to it.

One return is in the bonus room by the thermostat. The other 2 are in the hallway at the top of the stairs. 

The problem is that my kids all sleep with their doors closed. At night the bonus room is nice and warm but the kids are freezing 

I'm wondering if I could add small (12"x12") returns in each of the 3 bed rooms. I could take one of the 12" return ducts at the top of the stairs and split it into two 8" ones and run them to two of the bedrooms.
I could then split the one in the bonus room with the last bedroom the same way.

The two 8" ducts have about the same area as the one 12" duct so the flow would be about the same?

My kids are looking forward to your response 

D2.


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## beenthere (Oct 11, 2008)

An 8" round has 50 sq in cross section
A 12" round has 113 sq in cross section.
Although 2-8" are close in cross section. The small difference makes a big difference. Along with the fact that they also have more surface area for less cross section.
At a fixed .1" friction rate, an 8" round sheet metal duct has a rating of 240 CFM.
A 12" at the same friction rate has a rating of 700 CFM. 

Your idea would starve your system, and cause lots of trouble.

Good chance, you are already short on return.

Best thing. Is ADD new returns to the bedrooms, and leave the existing ones alone.
When the bedroom doors are closed. The new returns will draw in air.
And you will find that the supplies blow in more air.


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## Dutch2 (Oct 20, 2009)

beenthere, thanks for your reply.

The bedrooms are about 12'x14'. Can I just add a 12"x12" ceiling return in each room?

Should I use 8" duct from there to the existing flexible 12" duct? What is the best way to connect the new duct to the existing one?

Thanks again,

D2.


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## beenthere (Oct 11, 2008)

The 12X12 return grille is fine.
An 8" duct for it will probably be fine.

DO NOT connect it to the 12" duct from the hallway or bonus room returns. Run it all the way back to the return plenum at the furnace/air handler.

If you connected the 8" to the existing 12". You would just decrease the amount of return the furnace/air handler can get from the new returns. Sort of defeating adding returns.


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## Dutch2 (Oct 20, 2009)

I just checked the attic and it turns out that one of the air returns at the top of the stairs goes to the downstairs unit.

In other words, I have only two 14x20 returns upstairs. Each one has a 12" flexible duct going back to the upstairs unit.

The two 12" return ducts are connected to the left and right of the unit. For the three new 8" return ducts can I disconnect one of them, add a duct board box, and connect the 12" and three 8" ducts to it?

Thanks for all your help,

D2.


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## beenthere (Oct 11, 2008)

If you make it big enough, you can.

You said left and right. Usually, that leaves a center position open for you.


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## Dutch2 (Oct 20, 2009)

Both units are in an open area in the attic, no obstructions around them so no reason why they wouldn't use the back of the unit.

There is a large Centrifugal Blower in the bottom of the unit where the returns connect. The back of the blower is pretty close to the back of the unit so there would not be a lot of room for the air to flow. I'm guessing that's why there are no ducts on the back.

A funny thing I noticed is that on the downstairs unit there is a large flexible duct (14"?) going from the top of the unit right into the air return box at the bottom. Doesn't that connect the hot/cold air directly to the return???

The downstairs unit has two zones if that matters.

Confused now 

D2.


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## beenthere (Oct 11, 2008)

Post pics of both units.


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## Dutch2 (Oct 20, 2009)

This is the upstairs unit with the two returns. The duct on the top right is not connected to this unit.









As I was typing in yellow I couldn't see it and I typed "fron" instead of "from"  This is the front of the downstairs unit. the duct on the right comes from a return. The box on the left has two returns going in it.
But there is another duct connected to this box...









Same box, same ducts... with one more duct going from the return box all the way to the top where other ducts come out and go to registers... huh?









Maybe hard to see, but this is the inside of the downstairs unit where the return ducts come in from the left and right. There is not a lot of room behind the blower which is why I think there are no returns on the back.

I'm really curious what the duct from the top to the bottom of the downstairs unit is for 

D2.


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## beenthere (Oct 11, 2008)

Is the downstairs unit zoned. Could be a bypass for it.
If its not zoned. then no idea why they would have done such a thing.
And I would put a manual damper in it. Shut teh damper, and see if the furnace operates ok. They may have over sized it. And had noise in the duct system. And that was their half a$$ solution.

Second floor unit. What a crappy return install.
The return opening into a furnace. Should be basically full size of the cut out on the furnace. That gets rid of, or atleast minimizes turbulance at the blower.
Build a plenum box on each side of that furnace. And on the side opposite of the blower motor. make that the side that the new returns tap into.

Should also do the same as far as a return plenum on the right side of the first floor unit.


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## tinmanrob (Aug 9, 2009)

Am I missing something?
Where are the returns filtered?
At the grilles?
I'm not familiar with attic installs.


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## beenthere (Oct 11, 2008)

Thats where they should be in that install.


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## Dutch2 (Oct 20, 2009)

The returns are filtered at each of the grilles.

The downstairs unit is split into two zones. The left and right duct coming out of the top each have a damper (if that's what you call it) with a motor that is controlled by the zone system.

I could add a damper in the bypass and experiment with it. What is a bypass for in the first place? Is there somewhere I could go read about that?

From what I understand about the returns is that they should always be connected to a box that is connected to the side of the unit, and that the whole side of the unit is open to the box, not just a 12" hole.

Thanks for all your help,

D2.


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## beenthere (Oct 11, 2008)

A bypass is used to maintain proper air flow through the furnace when only one zone is calling for heat or cooling.
There should be a damper in it already. A barometric, that is set to open when only one zone is calling. And closed when both zones are calling.

Yes, a full opening on the side of the furnace eliminates turbulance. And helps keep static pressure down, so the blower can move air easier.


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## Dutch2 (Oct 20, 2009)

I'll look for a damper in the bypass duct tomorrow. Is this going to be a damper that is electrically controlled? What do I look for?

I'll start my project by adding a box to the upstairs unit to create more space for the 8" returns from the bedrooms. 

:thumbsup:

D2.


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## beenthere (Oct 11, 2008)

Probably will just be a barometric. So it will kust have an arm with a weight on it, no motor.


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## Dutch2 (Oct 20, 2009)

You're right, there is a barometric damper in it with an arm with a weight on it. The weight is all the way at the end of the arm.

The damper opened when I turned one zone on, but it stayed open when I turned on the second zone. From what I understand the damper should close when both zones are on.

With only one zone on I could close the damper with my hand but there was a lot of resistance. With two zones on it seemed a little easier to close so it seems to me the weight isn't adjusted correctly. They ran out of arm and gave up.

I found "Setting a Barometric Bypass Damper" at http://www.zonecontrolblog.com/the_zone_control_blog/2008/03/setting-a-barom.html

Should I try to adjust this damper? 

Thanks,

D2.


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## beenthere (Oct 11, 2008)

It should close with both zones calling.
The main reason those dampers don't close when both zones are calling. Is the return is under sized. And or the supply duct.


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## Dutch2 (Oct 20, 2009)

Since this is for downstairs and the unit is in the attic I can't really change the supply or return.

Should I try and add more weight to the damper arm so it closes when both zones are on?

D2.

This HVAC is like a can of worms


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## beenthere (Oct 11, 2008)

Nope. That would be the worse thing to do.
Since it would lessen the amount of air over the heat exchanger and evap coil.
cause premature failure of the heat exchanger. And freeze up conditions of the evap coil. That could lead to damaging the compressor.


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## Dutch2 (Oct 20, 2009)

Thanks for all your feedback.

It sounds like I'll just add the bedroom returns to the upstairs unit and worry about the downstairs one later.

D2.


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## Dutch2 (Oct 20, 2009)

I'm not sure if I should start a new thread for this, but this is what I'm thinking about using to add the three returns in the bedrooms.

First a Duct board Return Air Box ($49)








http://www.budgetheating.com/Duct_board_Return_Air_Box_p/148005.htm

8" Starting Collars to attach the flexible duct to the box ($2.90)








http://www.comfortgurus.com/product_info.php/cPath/155_220_219/products_id/1600

12" x 12" Return Air Filter Grille in the ceiling of each bedroom ($26.50)








http://www.comfortgurus.com/product_info.php/cPath/105_136_175/products_id/3663

Can I use a 12" Ceiling Box ($11.43) on top of the filter grilles and then use the same 8" Starting Collars ($2.90) to attached the duct?








http://www.comfortgurus.com/product_info.php/cPath/155_220_184/products_id/1606

Or should I get a 12 x 12 x 8" Ceiling Box like this ($23.84)








http://americanhvacparts.com/Mercha...=CEB12X12X8&Category_Code=duct-return_air_can

Any feedback on this would be greatly appreciated 

Thanks in advance,

D2.


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## beenthere (Oct 11, 2008)

I can't get those links to work. Firefox is having trouble for me today.
But, yes, you can just use 12X12 duct boxes for the 12X12 return air filter grille.

If you use those 12X12X8 ones. You also need to insulate them


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## Dutch2 (Oct 20, 2009)

I added some pictures...


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## beenthere (Oct 11, 2008)

The duct board return is what you want, along with teh filter grille you show.

How ever. That collar is a collar for sheet metal. You need one that has a flange around it. Or it will not seal right.


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## Dutch2 (Oct 20, 2009)

OK, I see what you mean, the collars that go into the duct board box need to have a flange. I'll look for those.

One other thing I'm wondering about, will these two work together?









In other words, can I mount the grille in the ceiling and then the ceiling box on top of that to attach the flexible duct?

Thanks,

D2.


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## beenthere (Oct 11, 2008)

Yes you can. But, you MUST insulate the box, and of course seal it to the ceiling so it doesn't draw in attic air.


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## Dutch2 (Oct 20, 2009)

Better? 








http://www.budgetheating.com/Tab_Collar_p/146005.htm

As you can see in the pictures my attic is full of blankets and blown-in insulation. Is it enough to cover the return grilles and boxes with this, or is there something else I should do?

D2.


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## Dutch2 (Oct 20, 2009)

I'm not too sure about americanhvacparts.com and it's the only place where I can find the 12"x12" box with the 8" collar attached.

How about using a self-adhesive collar with a regular 12"x12" ceiling box?











D2.


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## beenthere (Oct 11, 2008)

Dutch2 said:


> Better?
> 
> 
> 
> ...


Yep, thats the collar.


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## beenthere (Oct 11, 2008)

Dutch2 said:


> I'm not too sure about americanhvacparts.com and it's the only place where I can find the 12"x12" box with the 8" collar attached.
> 
> How about using a self-adhesive collar with a regular 12"x12" ceiling box?
> 
> ...


You can use that box. but you have to bend flanges on it to seal to the ceiling. Or box it out.
And the self adhesive collar MUST be screwed fast. Or some where down the road it will come off, and suck in attic air.


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## dash (Oct 25, 2009)

beenthere said:


> You can use that box. but you have to bend flanges on it to seal to the ceiling. Or box it out.
> And the self adhesive collar MUST be screwed fast. Or some where down the road it will come off, and suck in attic air.


 
Not the case at all,some self adhesive collars willn last the life time of the duct system.
!

But,screws wouldn't hurt.


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## beenthere (Oct 11, 2008)

dash said:


> Not the case at all,some self adhesive collars willn last the life time of the duct system.
> !
> 
> But,screws wouldn't hurt.


Haven't had a trunk system come to the end of its life that had self sealing collars.
So I'll take your word on that.

But, I put screws in all of them.


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## Dutch2 (Oct 20, 2009)

Do I use mastic to seal the ceiling box to the return grille?


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## beenthere (Oct 11, 2008)

You can use mastic, or regular caulk. I use caulk.


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## Dutch2 (Oct 20, 2009)

Caulk sounds easier 

One thing I'm worried about is how to insulate the return grille boxes.

I understand that I have to do this because moisture will condense on the cold box in the summer and cause ceiling issues. What is the best way to do this?


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## spyder24 (Mar 28, 2010)

Did you ever finish this project? Any pics?


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## Dutch2 (Oct 20, 2009)

I finished it and it worked out well 

First I removed the old duct and measured the cutout for the box...










With the right cutters it's not that hard to make a big hole...










I attached the box to the side of the heater and re-attached the existing duct...


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## Dutch2 (Oct 20, 2009)

This shows the 3 new 8" ducts attached to the box...










This is the ceiling view of a new return vent. I covered it with a lot of insulation...










The vents are only 12"x12" but it has made a big difference in the bedrooms.

I'm planning to add bigger one to the master bedroom but that one is 50 feet away... I guess I should do that now while it's still cool outside.


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