Return ducts make a howling sound

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Old 06-05-07, 10:14 AM
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Return ducts make a howling sound

Does anyone know how to resolve a “howling” sound in the return air ducts of a forced air gas heating system? I have noticed that when I close the door of two bedrooms the howling sound will increase. Opening these doors again will reduce the amount of howling. It seems like the return duct work is acting like a large flute and the howling will change in intensity as the amount of airflow in the return ducts is varied.
 
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Old 06-05-07, 06:03 PM
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Quick & easy test

Remove all of the return grills then turn the system on. If the noise is gone, you need to find less restrictive grills. If the noise is still present, you are probalby going to need more or larger return ducts.
 
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Old 06-06-07, 02:55 PM
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Another thought.....

Thanks Grady! Removing the grills made little, if any, difference. For what it is worth, the airflow into any return point seems quiet and unrestricted without the whistling sound you might expect from other systems. I have a theory: My house uses floor joist space for return air. These floor joists cavities are closed-in by foil sided cardboard that is stapled into place. Is it possible one of these cardboard devices is leaking air and causing the howling sound? Think of the Good and Plenty box we had as kids and blowing into one end that is open. The other end would make a sound like that of the howling sound I hear in my system today. Just a thought in case you have more guidance to share.



Hard work is for those who are short on talent.
 
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Old 06-06-07, 03:47 PM
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I have noticed that when I close the door of two bedrooms the howling sound will increase.
Do the doors clear the floor or rugs by 2 ". They have to if you dont have return grills in the rooms there..
 
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Old 06-06-07, 06:10 PM
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Two bedrooms have their own return

To Ed Imeduc:

I forgot to mention the two bedrooms that are closed-off both have a return air vent that shares a single duct on a common wall. The gap at the bottom of each door is cut closely to the carpet. Sorry I didn't mention this earlier.
 
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Old 06-06-07, 07:46 PM
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Cardboard Panning

I know the stuff you are talking about & I guess it is possible that it could create the noise. We are not allowed to use it here nor are we allowed to just pan off a floor joist for returns. All returns must be actually ducted.

You could try taking that cardboard down & using either metal panning material or strips of ductboard.
 
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Old 06-06-07, 08:36 PM
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How many and where are all the returns?
 
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Old 06-08-07, 08:55 AM
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More information to consider

Grady:
As last resort, I will be more than happy to replace all of the ducting with quality materials. Until then, I will continue to locate and seal every "possible" leak I can find with hopes the howling sound will be resolved. I have a sneaky suspicion the foil covered cardboard material is "fluting" at a leak point - but I have not found the leak in question. A lot of the joints have already been poorly sealed with a grey colored liquid sealant that was applied with a brush.

Jay11J:
There are a total of 4 returns. A large return is located in the living room and another large return in the master bedroom. Two more returns are found in the two other bedrooms and share a common duct. Please keep in mind that all of the return ducts have a nice slow air flow and don't seem to be tasked as there is no sound of rushing air.
 
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Old 06-08-07, 05:44 PM
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Noises, Grrrrrr

Noises & smells are the two hardest things to fix, especially online since we can neither hear nor smell what's going on.

You say the air flow is gentle & no sound of rushing air. Have you pulled the blower & examined it? There could also be something in the return plenum just upstream of the blower? While you have the blower out, stick your head in there & have a peek.
 
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Old 06-23-07, 06:53 PM
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Offending "howling" noise has been discovered

It seems that I have discovered the problem that caused the howling sound in my return air ducts. The process of finding the howling sound was a bit confusing because when one of the two large grills in my home was removed, the howling continued. However, when I removed both large grills at the same time, the problem was resolved. I also discovered that when I applied a slight pressure with my hand at various points on the grills, the tenor of the howling sound would change! I plan to replace the two offending 1/4 inch slotted grills with 3/8 inch slotted grills. This, I hope, will keep things quiet. Otherwise, I will adjust the fan to a slower speed - thus reducing the airflow to a speed that will not cause the grills to be resonant - I hope.
 
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Old 06-24-07, 07:58 PM
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Return Grilles

Replacing them with less restrictive grilles is a good start & hopefully will take care of the problem. If it does not, don't just slow down the fan speed without measuring temperatures. Too little air flow can create big problems.
 
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Old 06-26-07, 03:33 PM
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I also discovered that when I applied a slight pressure with my hand at various points on the grills, the tenor of the howling sound would change! I plan to replace the two offending 1/4 inch slotted grills with 3/8 inch slotted grills.

Ah yes the good old grill that resonates. Sometimes you can take and bend the small bars on them more flat like and that helps stop the noise.
 
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