# Air return makes too much noise, what should I do?



## bigburb (Jun 12, 2008)

I have a 4 ton AC system with 2 16x25 returns. One is located directly under the AC and is attached to the plenum, the other is located about 15 feet away and is attached via about a 10" duct. The closer one makes a lot of noise and catches most of the dust... the farther one has hardly any suction (I can usually go about 6 months b/t filter changes). I know I need to get more filter area somehow, I had three theories on what to do, but would like input:

1. Enlarge the current opening to 16x32, this would yield 175 sq in more intake space.
2. The chase directly under the plenum is on a hallway corner, I could install another 12x24 return grill on the adjacent wall that would yield 288 sq in. However I wasn't sure if it would be "aesthetically pleasing" to have a return on either side of a corner.
3. I can enlarge the return duct from the furthest chase to 12", I'm not sure if this would have enough effect to make a difference though.


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## zootjeff (Jul 11, 2007)

bigburb said:


> I have a 4 ton AC system with 2 16x25 returns. One is located directly under the AC and is attached to the plenum, the other is located about 15 feet away and is attached via about a 10" duct. The closer one makes a lot of noise and catches most of the dust... the farther one has hardly any suction (I can usually go about 6 months b/t filter changes). I know I need to get more filter area somehow, I had three theories on what to do, but would like input:
> 
> 1. Enlarge the current opening to 16x32, this would yield 175 sq in more intake space.
> 2. The chase directly under the plenum is on a hallway corner, I could install another 12x24 return grill on the adjacent wall that would yield 288 sq in. However I wasn't sure if it would be "aesthetically pleasing" to have a return on either side of a corner.
> 3. I can enlarge the return duct from the furthest chase to 12", I'm not sure if this would have enough effect to make a difference though.




If you can fit a 4" thick filter (available at Fred Meyer, online, etc) That is one way to increase surface area.

Put in an inline filter above the furnace unit and toss the return register filters.

Best way to reduce sound is to turn corners in the duct work. Also putting 1" insulation on the inside of the plenum can help.


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## bigburb (Jun 12, 2008)

So you're saying I can fit a 4" filter in a 1" grill? I saw 16x25x4 filters at the box store but I figured I needed a different grill to fit it.


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## biggles (Jan 1, 2008)

block off the one under the unit by half so it starts to pull that 15" run back more..is the furnace in a louvered door room or 100% open that 15 run seems more the true house return.if you want to go with 4" filter to catch the dust it can be done you can go with a 2" pleated 1" pleated also check out local Grainger supply they welcome home owners...the unit is basically pulling the most air from the nearest source as it should and the filter differece is the proff:whistling2:


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## bigburb (Jun 12, 2008)

The 15' run is located in the living room, which is a more "central" location to the house, but the one directly under the unit is in a hallway near bedrooms with no obstruction to the rest of the house. I found the Honeywell FC40R1060 which has a 1" lip so I can retrofit it into my existing opening. I might try this first... who knows if this is more than enough I might just block off the 15' run and use that space for something else.


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## biggles (Jan 1, 2008)

which return is the thermostat nearest to shold be nose hi right above the return or in the general area.when you set temps its the return that satisfies the stat not the discharge on the supply grills...but that return pulling over it:wink:.maybe consider half on both for a true'r return...just do one test at a time to see the differences:thumbsup:


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## bigburb (Jun 12, 2008)

Thermostat is directly above the hallway return, which is the one under the AC system.


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## bigburb (Jun 12, 2008)

What kind of insulation should I use to insulate the chase? I know standard fiberglass would probably be a no-no


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## biggles (Jan 1, 2008)

OK thats makes it easy block the 15' run for total air pulling over that sta for a true setpoint cycle.would you say the hallway is more a common area then that 15' return grill location if so..i could suggest relocate the stat to nose(average 6' person) hi over that 15' return grill but thats too much seems the 15' is useless except for holding spare filters i'm not crazy about 4' filters in residential 1 or 2 is cool if dust and allergies are a problem..monkey with it lets here back:wink:


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## bigburb (Jun 12, 2008)

I went ahead and ordered a 4" filter. It was only $10 more than the 2" filter but it will last another 6 months (supposedly). After installing it, I plan to block off the chase on the 15' run and see how it does. 

I'd like to get some duct liner to quiet down the chase some, but dang its expensive! Is there anything cheaper out there?


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## bigburb (Jun 12, 2008)

Would something like this work? http://www.soundprooffoam.com/quiet-batt-insulation.html


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## Norlure (Jun 4, 2011)

*Return duct*

Hi !

Your existing ducts are 16x25 (400 square inches).if you use 2" insulation inside the duct,you'll end up with only 12x21 (252 square inches).

I would keep the other duct work.


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## bigburb (Jun 12, 2008)

No I just mean insulating between the 2x4's inside the chase.


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## Norlure (Jun 4, 2011)

*Noisy duct work*

Hi !

In order to reduce the noise coming from the duct work or to get ride of it ,you must line the inside of the duct with the proper insulation.

Many time on commercial job site we have to do the first 10 feet coming from the unit or sometime the whole duct work system.

If an engineer ask for the duct work to be lined with accoustic and the dimension is 14 x 23,we have to make the duct work 16 x 25 for 1" accoustic lining.

You'll see a world of difference lining the inside.If you do the outside I am pretty sure you are waqsting your time and money.

Glad I could help.


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## bigburb (Jun 12, 2008)

Yes I plan on insulating the inside, I think I'm going use that cotton stuff I linked to. I may not have been clear enough in my terminology - my AC chase is a wall cavity, with a small plenum on top leading to the unit. The inside of the plenum is insulated already. What I proposed doing was lining the inside of the wall cavity, between the studs, with insulation. I'm not restricting it anymore than it already is, just going between the studs.


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## bigburb (Jun 12, 2008)

Installed the 4" thick filter yesterday, DEFINITELY cut down on the noise. No more whistling or loud suction noise. However I can still hear noise from the chase, so I still think I'm going to insulate it (will probably tackle that next month). 

In the winter months, maybe when its cooler in the attic, I plan on suspending the handler from the roof rafters.


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