Baffle design to reduce noise of return

[504 Tailwaggers]

I have an extremely noisy air return located at the entrance to my living room. It drowns out conversation and even the TV. I've looked through some of the posts here and I realize that the ideal thing would be to have a lot of duct between the return and the furnace, but I don't really have that option here. A friend suggested putting a system of baffles in the return to force the air to make some turns, he says it should reduce the noise quite a bit.

I whipped up a 3D model of a baffle system for my return and attaching it here, along with a photo of the return with furnace sitting directly above it. Im in a 1000 sq ft "shotgun" style house, return is just above floor level, furnace/coil sitting on top of it, all the vents are in the ceiling. The return cavity is quite large - about 20"(w) x 38"(d) x 32" high - but the grill and filter for it are only 16x24. (Yes, about 4" of the 24" grill are obstructed by drywall as seen in photo.)

I don't know the specs for my system but I do know the model number - it is a Payne PG8DAA. There is another piece of paper showing a model PA10 but I don't know what that is referring to. The filter size for the return is 16x24. It sucks air in like a tornado!

I wonder:
1) What do you think of this baffle system, do you have any design suggestions?
2) I could cut a second intake hole into the wall of the return directly opposite the existing one, would that be beneficial?





Thanks for any advice.
Dan in New Orleans

[doug1111]

,nice drawing with measurements how did you do this?? Sorry I cannot help you with your answers someone will chime in soon I am curious myself if your design will work?

[vstech]

With the large return you have, the baffles you are planning should dramatically help. However, metal, or wood will not work. You will need a contractor to build it out of duct materials.

[504 Tailwaggers]

I created the 3D drawing in Google Sketchup - its a free program you can download:
sketchup dot com / products / sketchup-make
(take out all the spaces and replace "dot" with "." Since I am new to forum, it won't allow me to post links!)

[504 Tailwaggers]

I actually am planning on constructing the baffles out of this 1/2" thick insulating foamboard sheathing they sell at home depot called Foamular, it has R-3 thermal rating but I was told it was the best thing they had for sound absorption. Going to affix it to the inside walls of the return and leave some slots where the baffles, same material, will fit. Maybe Lowes has something better?

Im really wondering if I should add another inflow grill to the opposite side of the return, if having more draw will help cut down on noise and maybe increase efficiency some? This is where I have absolutely no experience.

[Hrdworkingacguy]

Just keep in mind a return is only as big as the smallest opening...if your baffle chokes down to a opening smaller then the unit requires for cfm you can starve the system(though it has to be pretty drastic)...

[doug1111]

I created the 3D drawing in Google Sketchup - its a free program you can download:
sketchup dot com / products / sketchup-make
(take out all the spaces and replace "dot" with "." Since I am new to forum, it won't allow me to post links!)

thank you for the info Google SketchUp. very interesting thread learn something everyday.

[doug1111]

Hrdworkingacguy - return is only as big as the smallest opening. I have heard that before but don't understand it. on a vacuum pump why is it beneficial to have a large hose when it hooks into a small Schrader port? And for 504 tailwaggers would it be a good idea beneficial for him to put in a nother return grille??

[504 Tailwaggers]

My existing inflow opening is really only 16"x20" (even though grill is 16x24) because whoever constructed this return obstructed the opening with a 4" thick additional drywall, you can see it in the photo. Maybe it was necessary to support the furnace above it. Anyways, I don't know how to calculate the necessary cfm but I wonder if I put another opening on opposite side, it might slow down the airflow and help reduce noise, not to mention increase efficacy of the unit. Ive heard of returns being too small - can they be too big? Doesn't the size of the "coil" have something to do with this too?

[kdean1]

Line the cavity with duct board.

[vstech]

the noise you are hearing is coming from the blower itself. adding a second inlet grille will not help with the noise. the baffles will, as long as there is good liner in the box, no smooth reflective sides, and the sound has something to bounce off of, and get absorbed by.

do not make any obstructions that are smaller than twice the furnace opening size. I STRONGLY recommend you get a contractor to do it, with proper ductwork materials.

[energy_rater_La]

don't use foam in the return.

I'd start by lining the return as suggested above,
with duct board.
sides & bottom should be covered with ductboard
with fg side facing into the return to absorb sound.
paint the mastic on the walls of the return, then set the
duct board into the mastic. once lined...mastic the
joints.

while you are working around in there...seal the sides
of the return.
I can see the leakage from here!
on the right side the opening at the lower
side of the r/a filter grill. on the left side seal the opening
between the 2x & whatever is to the left of the 2x.
take a look at the top of the r/a filter grill. if it is an
opening into the wall...seal it up.

sounds like a trip to the hvac supply is in your future.
I'd use low R-value ductboard...R-4.2 if you can get it
or R-6. you don't need the R-value but don't want to
lose too much of the size of the return.
bucket of paint on mastic & chip brushes should
set you up...and maybe some caulk.

best of luck.

[firecontrol]

Does the noise change at all when you take the grill front off?

[energy_rater_La]

what size system do you have & what size is the r/a filter grill?

you have room to increase the r/a filter grill & filter.

oh I see...16x24. you can't have too much return.
my 2 ton system has a 24x24 r/a filter grill.

what is your location?

best of luck.

[Poodle Head Mikey]

Start off with the concepts:
1. You want slow air speeds and big ducts / low velocity.
2. You want a convoluted sound path.

First: has the system been air balanced with the purpose of reducing the air flow to the lowest correct amount of air volume? Or did the installer just set the blower on high and take the check? Perhaps a lower blower speed can be used? The ideal would be a large blower operating at low speed blower to acheive the required air volume. Too late for that now but keep the concept in mind as you work.

1. You want to 'confuse the sound waves'.
2. You do not want to create any pinch-points for the air flow.
That is: do not make any portion of the air flow path smaller than the opening to the bottom of the furnace.
3. Angled surfaces are your friend in this endeavor - you want to confuse the sounds waves / bounce them around / make them work to escape.
4. You want to absorb rather than bounce the sound - so line the plenum with sound absorbing material and cover the baffles with it as well.

I like the 'build a decorative column' for the air handler - I am going to steal that idea. But I would have returns on all available sides. Is this system for A/C as well? If so I hope you have ceiling fans in all the rooms - that low air return will badly compromise cooling performance.

I assume this is a rancher style house? Is there a garage? Could the air handler / furnace have been installed out there? That's what I typically do. Are all the air ducts inside the conditioned space? In a soffit? Or do they go up into the attic space?

PHM
----------

I have an extremely noisy air return located at the entrance to my living room. It drowns out conversation and even the TV. I've looked through some of the posts here and I realize that the ideal thing would be to have a lot of duct between the return and the furnace, but I don't really have that option here. A friend suggested putting a system of baffles in the return to force the air to make some turns, he says it should reduce the noise quite a bit.

I whipped up a 3D model of a baffle system for my return and attaching it here, along with a photo of the return with furnace sitting directly above it. Im in a 1000 sq ft "shotgun" style house, return is just above floor level, furnace/coil sitting on top of it, all the vents are in the ceiling. The return cavity is quite large - about 20"(w) x 38"(d) x 32" high - but the grill and filter for it are only 16x24. (Yes, about 4" of the 24" grill are obstructed by drywall as seen in photo.)

I don't know the specs for my system but I do know the model number - it is a Payne PG8DAA. There is another piece of paper showing a model PA10 but I don't know what that is referring to. The filter size for the return is 16x24. It sucks air in like a tornado!

I wonder:
1) What do you think of this baffle system, do you have any design suggestions?
2) I could cut a second intake hole into the wall of the return directly opposite the existing one, would that be beneficial?





Thanks for any advice.
Dan in New Orleans

[energy_rater_La]

I missed the part where you said you could add another
r/a on the other side. might be the easiest solution.
but still...air seal that return!!

best of luck

[504 Tailwaggers]

Firecontrol, the noise does not change one bit with the grill off. But I did slide in a piece of foamboard, angled down from the top of the grill, as a test to force the air to move down towards the floor and then make a sharp turn upward toward the furnace, and it cut down the noise level quite a bit. Hopefully in combination with insulating the return walls and sealing up leaks, it will cut the sound even more without damaging performance.

So Im going to go ahead with my baffle plan as illustrated. Will look for some duct board as suggested above by energy_rater_La, but I don't quite understand why I should not use this pink insulation board I bought that people at HD said would be good for sound absorption.

[lkapigian]

I would add additional returns on the sides, looks like you could have up to 4, line as mentioned above- install Bar Type returns not stamped faced filter grills raise the furnace and put a base below it--

Also set your fan taps to the speed needed to match the design CFM

OR.............Turn up the television , that would be my solution

[504 Tailwaggers]

I just realized there was a page 2! Sorry, only now just read the posts on this page.

I do not know what this system is rated at - bought the house a year ago and HVAC came with it. Got a few quotes for moving it up into the attic but was way too expensive. House is a 1100 sq ft New Orleans "shot gun" style house - no hallways, must travel through every room to get from front to back. No garage.

I will try to look up the specs on this HVAC tonight if I have time - all I know is the model is Payne PG8DAA and some other booklet by the furnace has Model PA10 written on it but it is so damaged I can't tell what its for!

[energy_rater_La]

glad you kept the unit out of the attic.
bad enough that the ducts are up there.

can you give us the model numbers from the
condensing unit outside? that will tell us the
size & thus the amount of return air needed.

the reason for not using the foam board
in the return is that it isn't an approved material.

granted, the return air isn't going to be warm enough
to cause foam to offgas, but any pro would use
approved materials.

attaching the foam board as you show raises questions.
how would you hold it in place long term?
if either piece comes lose it could block off the
air flow to the coil, and that would be a very bad
thing.

lining the return with ductboard or creating another
return air opening within the same r/a area
would be your best options.

ductboard is easy to install. measure twice,
cut & install. all you need is a razor knife, tsquare
& mastic. a few roofing nails to add extra
holding...easy peasy.

always use approved materials.
astm isn't really just an acronym for
another stupid testing method.

and HD knows little about hvac standards.
not their area of expertize.

you should also think about sealing the ductwork
in the attic. once it is cooler that is.
average duct leakage is 30%.
if you have a 3 ton unit...that is 1 ton of
leakage before it even gets into the living space.
plus your visible return leakage of course.

thought you might be a New Orleanian when
you said shotgun house. I've lived in quite a few
there in the crescent city. good times for the most part.

best of luck.