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Old 02-08-2012, 12:43 PM   #1
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Return-air Sound Proofing


Hi there,

We had a new furnace and ductwork installed in our 1940s bungalow. The basement ceiling is currently open, so we have full access to everything below, but will be finishing the ceiling and boxing in the ducts in the coming months.

Our installed used 2x 16'' OC joists to create a return-air run, using sheet metal. The return air run is about 8 feet away from the furnace.

The return air can get quite noisy when the blower is on high (which is not often, but is none-the-less annoying). The noise is a combination of "whooshing" air (I would say about 75% of the noise level) and fan noise (about 25% of the noise level).

I am looking for some assistance/suggestions for how and what to soundproof the return air with, as well as something to wrap/stick on the duct trunk running the length of our basement (as I would like to minimize sound transmission from the basement to other rooms in the house through the ductwork).

Thanks in advance,

Dave

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Old 02-08-2012, 02:37 PM   #2
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Return-air Sound Proofing


certainly not an expert here, but if it was me, I would have the contractor come back out.

If you could give us a model number and MFGR that would really help. Or even if you could tell us if this is a heater, a heatpump or a straight ac system and of course how many tons...

The idea here is that a 2 inch by 16 inch duct can only flow so much air. Return air noise is sometimes caused by fast Feet per second movement of air. I believe that a fair rule of thumb is about 250 to 300 fps. This allows the air to be slow enough for the filter to work. The lower the FPS, the lower the air whoosing will be.

so by telling the forum what equip etc you have, they can, I hope, figure out if the 2 x16 duct is too small.... of course I could be all wet...


LOL

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Old 02-08-2012, 02:41 PM   #3
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Return-air Sound Proofing


How many returns do you have in the house? If you only have 2 joist spaces used (i'm presuming they are side by side) is there only the one return location? The noise is likely due to an inadequate amount of return air coming back to the furnace, which is cauing high velocities through the grill of your return air registers.

Could you add additional return air vents to your house since the basement is still open to add additional return ducting and registers? If you have enough return air registers and ducting it should quiet the system down to where the air coming out of your supply registers is more noticable than the returns.

Last edited by HVACDave; 02-08-2012 at 02:44 PM.
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Old 02-08-2012, 03:45 PM   #4
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Return-air Sound Proofing


Quote:
Originally Posted by HVACDave View Post
How many returns do you have in the house? If you only have 2 joist spaces used (i'm presuming they are side by side) is there only the one return location? The noise is likely due to an inadequate amount of return air coming back to the furnace, which is cauing high velocities through the grill of your return air registers.

Could you add additional return air vents to your house since the basement is still open to add additional return ducting and registers? If you have enough return air registers and ducting it should quiet the system down to where the air coming out of your supply registers is more noticable than the returns.
Currently there is only one return air (using 2 joist spaces for a conduit, as mentioned) about 30'' long by 6'' wide. We are planning on putting a 2nd return air in the basement to balance the circulation (1 return on the main floor, 1 in the basement.....it's a small house). This will be built inside the furnace room wall, once we build the wall. Our installer has left sheet-metal installed over another set of joists, creating a conduit for another return air, where we will be building the furnace room wall.

My concern is that adding the 2nd return air will not quite down the "whooshing" due to the distance between them and the furnace.

Our furnace is a Bryant Evolution Series 355AAV042060. We also have an AC unit (Bryant Legacy 113ANA024), but haven't used it yet as we had this install done in October (I'm located in Toronto, ON, Canada).
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Old 02-08-2012, 03:59 PM   #5
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Return-air Sound Proofing


Return is too small. Add another one upstairs.
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