Home A/C Return Air Noise

The rush of return air flow through my plenum cover and air filter is very noisy and I am wondering if the builder left out some noise reduction feature. This is not 'mechanical' noise, but the 'wind rush' noise. The return filter opening is at floor level and the air makes an upward turn to enter the fan suction which is about 30-33 inches above the floor inside the return plenum. The filter size is 20"x25". The actual entrance to the fan is smaller, looks to be about 18"x18" (perhaps that hole is too small?). There is nothing between the filter and the fan suction; should there be some kind of 'noise reduction baffle' in that location? Any hints appreciated. Thanks,
--
John Hanley
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If you have velocity noise at the return filter grille, it could be a restrictive grille or a restrictive filter.
If you have a high efficiency filter like a washable plastic electrostatic filter or a pleated filter, they have a high resistance to air flow. Some of the air will bypass the filter if it is not a good fit in the grille or holder, causing a rushing noise.
If the fins on the grille are 1/3 inch apart, common on builder's grade, they tend to be noisy, especially if the area of the grille is less than 200 Square inches per ton. A 20 x25 grille will usually get noisy above about 2-1/2 tons. You can put in a steel grille with 1/2 inch fin spacing or an aluminum grille with 2/3 inch fin spacing to reduce air noise. Or you can install a larger grille or an aditional grille. If the vanes on the grille are opposed to the direction of air flow in a duct, you can turn the grille around to reduce noise
If you add baffles, you will reduce air flow, which will reduce the capacity and efficiency of the system. If you think you have too much air flow, find a contractor with an air flow hood or hot wire annemometer who can accurately measure air flow. Do not reduce air flow unless you are SURE that you have too much.
I am emailing you an article on high efficiency filters that I wrote.
Stretch
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too
often
there
The above alone is enough to discredit any advice you may give.
Obviously, you dont have one....yet you still can't keep your mouth shut....
--
SVL




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Call the fucking builder and stop bitching to us.........
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Assuming it's done to spec mechanically, perhaps the fan's just pushing too much air too fast? Not an exptert by any means, but I do know you can often adjust the pulleys (set screw on the motor pulley can make it bigger & smaller). Or, there is air supposed to be entering somewhere else? It almost sounds like all the air is being pulled in thru one opening? Usually there are more than one, sometimes several; are any closed off?
--
Let someone else do it
I\'m retired!
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I owned a house with a similar problem. The issues were 1) Sheet metal is a good radiator of noise. 2) The return was installed with a right angle bend that caused turbulent flow.
What I did was to pop rivet a radiused curve over the right angle in the ducting to reduce the turbulence in the airflow. Next, I purchased some sound deadening materials and applied them inside the return. The return was probably a cube of about 3' on each side.
These two band-aid fixes made a difference.
KB
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For only an 18x18 return its gonna have to be a real small furnace.... How about post the make/model/serial number of the furnace so we can find out what its rated for on the airflow and we're not just guessing here. Links to pics would be helpfull too.
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I had the same problem after having my 2 1/2 ton air handler replaced with a 3 ton unit 2 months ago.
With the gill open the noise went away.
So, what I did, was remove every other fin from the grill/grate, problem solved.
Keep in mind I don't have a "stamped" grill/grate. It is a heavy duty one made out of alumium. I took the frame apart and removed every other fin. That increased the openings from 3/8" to 3/4" between the fins. The ONLY thing I don't like about it is, you can now see the filter but after a while you don't even notice it.
As another poster recommended going with a commercial grill/grate should solve the problem. Just make sure the space between the fins is greater than what you have now.
Or, you could just (if you grill is stamped) cut out every other fin smooth the edges with a file and see if that takes care of the problem. You might want to try this first because those grills AREN'T cheap!
Also, to the poster that mentioned NOT to use a plastic electrostactic filter, that is what I'm using and it cut down on the wind noise significantly over pleated filters, while also keeping my unit, home and nose clean. : )
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noon air wrote;

I just had a Trane 3 ton air handler installed and the opening going into mine is about the same size.
Actually it's where the filter slides into for units that are installed inside the dewelling. ie; Apts, condos, depluxes, etc., NOT houses where the handler is in the garage. Although a house that doesn't have a garage has to have it installed in the house.
Apparently these "newer" air handlers are getting smaller. The foot-print of this new Trane is about 6" smaller than the 20 yr old 2 1/2 ton "Comfort Maker" air handler that I replaced.
Also, I have a heatpump and the emergency/aux heating coil is smaller than the one in my older unit (i saw it when they pulled the old unit) but according to the AC company it's the same size.
Bullshit, it doesn't even get HOT, it gets WARM.
Good thing I live in Fl! LOL
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Sounds to me (O.K., I can't hear it, but you know what I mean) like the ductwork was not sized properly. If the system has been "choked" down (improper return size or not enough supply vents) then you can get all kinds of noises.....
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On Thu, 21 Apr 2005 22:19:11 GMT, "Hi Ho Silver"

step 1) take the filter out of the return filter opening and see if that makes a difference.
step 2) with the filter in place, prop open the return air grill. see if that makes a difference. Is the return air grill of the "stamped face" variety, or is it of the "bar type" variety.
Builder model homes typically have cheap, stamped face supply and return air grills. These impose too great of a restriction on the air flow. Change them out to commercial grade bar type supply & return grills, and your air noise problems may go away.
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The furnace sounds awful big for the size house you have and the climate. Maybe get a load calculation done, your system may be too big.
Stretch
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Thanks for various suggestions. I did the test of running without the return air filter, and the wind noise is even worse that way. The wind noise is plainly coming from the fan per se.
A label on the unit "installers instruction manual" shows:
Consolidated Industries Lafayette, IN Mod # MBA 080 NH4R Serial # 990917039
My house is in Houston, TX and was built in 1999. The house has 1500 sq ft, is on one floor, and the furnace is in an alcove in the house (not in the attic). The unit handles both heat in the winter and a/c in the summer. I think the air flow with a/c must be higher than with heat, because the air wind noise is higher with the a/c. I have some pictures, and send them to you via email if you like.
Thanks,
--
John Hanley
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wrote:

Metal eggcrate grills are great for this problem. Most of the time in a direct return situation, the duct size isn't the problem, but the grill face is too small. Eggcrate grills obviously will have the least amount of grill face.
Rob
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