My cold air return too noisy. Please help!

[skaranam]

I apologize in advance for lack of my knowledge about HVAC systems and sorry for the long posting. I am trying to provide as much information as I can.

This is my first home and I moved in to this home in February 07. It is about 3500 sqft home with 2000 sqft in the first floor and 1500 in the second floor. It has two HVAC systems. First floor unit is in the basement and the second floor unit is in the attic. The first floor has 12 air vents but only one cold air return in the hallway. The HVAC unit is right underneath the hallway in the basement. The cold air return is connected to the unit with a big circular shiny metal duct about 2 feet in diameter. This duct is about 15 feet long in total with two 90 degree bends.

The cold air return is exceptionally noisy. It sounds like a giant vaccum cleaner. The noise level is same with furnace(winter) and AC(summer). When it comes on, it is really scaring little kids if they are near the duct. Because this is a new house, builder is still attending some of the issues ( I have a basement leak. That is another story). But for the noise, he says that he followed the design specification and there is not much he can do to reduce the noise.

As far as the make and model is concerned, it is a Goodman. The furnace model number is GMH8. This is the only number I could find in the material that builder gave me during closing. I went to the unit and looked for model number for the blower but did not find any. The whole unit looks like a tower with three units stacked on top of each other. There is a little sticker on the middle unit with model number as CAPF4860C6AA with serial number next to it.

Sorry for not providing much information. I can call the installer to get more information if needed.

But as mentioned above, the noise is really unbearable. I am planning to talk to the builder's senior management to escalate the issue. But I doubt, if they are willing do anything to fix the problem.

Is there anything I can do to reduce the noise. I hired a building inspector before closing and he said that I can use automobile sound insulation tape inside the duct to reduce the noise. What do you think about this option.

Before closing, I raised this issue and they added insulation around the duct and told me they added a grid inside the duct to reduce the noise. Not sure where they added the grid but, it didn't help much.

Is there any specification on max allowed noise for home units. I can get a meter and measure the noise in db if required.

Thanks for reading this long posting. Any help is highly appreciated.

[coolmen]

can you show some photos

[hvac_superman]

I would check the static pressure on the furnace. That will tell the story if your return duct work and air flow is adequate. You should be moving 400 cfm/ton

[skaranam]

I will post pictures tomorrow.

[pstu]

I had a new return added to my system (I'm a homeowner) and it was a bit noisy due to being a short length of duct with only a 90 degree bend. At the time I was only thinking about airflow and places to locate the return. It is my understanding that I may have made a mistake by not having longer and more bendy duct, more changes of direction, so that sound waves get dissipated on the duct walls. Or something like that. If a pro contradicts me, then I expect he is right.

Before that experience, I figured excessive noise would be due to air flowing at too high a speed thru the return duct. Or whistling past a small opening. Obviously I don't know whether either of these applies to your situation. I sympathise with your problem, am interested in the subject, and hope you can succeed in fixing it.

Best of luck -- Pstu

[Mr Bill]

It is my understanding that I may have made a mistake by not having longer and more bendy duct, more changes of direction, so that sound waves get dissipated on the duct walls. Or something like that. If a pro contradicts me, then I expect he is right.

I will not contradict you but I might add some food for thought, if you return is in the attic "as in big large flex return laying in attic" common sense would tell me yes the longer the flex the quieter the return may be, but you also will have more heat added to a longer return flex line than you would a shorter on, will a 20' pipe heated at one end hold more heat than a 5' pipe heated at the end?
My analogy here may be small as to the amount of heat picked up in a longer return, but only a good old test will bring out the truth.

[pstu]

Very true. Thanks for bringing it up.

Best wishes -- Pstu

[JBM1000]

High Static is the problem, no matter what size big pipe thing'y you see. Only if and when a correct test for it is done and a professional with experience sizes what you need will you have any results. Until then it's "The big jet engine".

[skaranam]

Here are the pictures.


This is the air return.

http://i206.photobucket.com/albums/b...m/IMG_1175.gif
http://i206.photobucket.com/albums/b...m/IMG_1173.gif
http://i206.photobucket.com/albums/b...m/IMG_1171.gif
http://i206.photobucket.com/albums/b...m/IMG_1172.gif
When the unit is running, I could feel the cold air rushing out the white plastic pipe (marked with red color arrow). Is it suppose to do that. I thought that it is a drain pipe for condensation.

http://i206.photobucket.com/albums/b...m/IMG_1174.gif
This is the duct connected to the air return.

[Mstrav]

when you open the filter grill cover does the noise go away? if yes, you need to to have that 20 x 20 filter grill replaced with a bar type filter grill, you can call your a/c company and ask if they will sell you one or at their convenience can swap it out, the stamped face you have is garbage and has much restriction in face area. I see this all the time, you may be hearing other system noise, but if opening the door with the filter in helps make the noise go away, then this is what I would do.

matt

[transportithere]

I am no technician.. But, is sounds as if you cold air duct is too small. The sound is negitive or low pressure.. Then again it could be the airhandler.. Many air handlers are noisy.. NEW homes are built to "code" not for comfort.
Some people have need to Upgrade thier system to suit thier life style.

The children will get over the noise. Although, memories are long as life..
Do you remember the cold, dark basement? or the cold spot on the back porch?

[Airmechanical]

I am no technician. Many air handlers are noisy.. NEW homes are built to "code" not for comfort.
The children will get over the noise.

hey we cant help it if your not a tech, airhandlers are not noisy if installed properly!

your advise on the children getting over or used to the noise is non productive!

there is a static pressure problem with the system that must be addressed!



.

[hvac_superman]

Do a static pressure test. That will tell you what's up. I wonder how that round duct runs through the floor and wall? Can you post a close up of the round duct as it penetrates the first floor? How wide is the wall where the duct is burried? Is there plenty of room that it didn''t get crushed?

[skaranam]

when you open the filter grill cover does the noise go away? if yes, you need to to have that 20 x 20 filter grill replaced with a bar type filter grill, you can call your a/c company and ask if they will sell you one or at their convenience can swap it out, the stamped face you have is garbage and has much restriction in face area. I see this all the time, you may be hearing other system noise, but if opening the door with the filter in helps make the noise go away, then this is what I would do.

matt

I opened up the grill and removed the filter but it didn't change the noise level. I feel like the noise is mostly air gushing in.

[mark beiser]

Need the model numbers of the equipment to be sure, but I seriously doubt that cutting a large round duct into one side of the furnace like that is one of the acceptable ways to connect the return to the unit per the installation instructions.

Even if a single side return is acceptable, there needs to be a particular size of rectangular cutout on the side of the furnace with a fitting so the furnace intakes air through the full size of the opening, not just a round hole with a duct tapped into it.

[skaranam]

Do a static pressure test. That will tell you what's up. I wonder how that round duct runs through the floor and wall? Can you post a close up of the round duct as it penetrates the first floor? How wide is the wall where the duct is burried? Is there plenty of room that it didn''t get crushed?

Here are some more pictures



Here are the pictures with the grill off.



Here is the picture from basement.

I watched the duct during construction. The enclosed space where the duct is installed is much bigger than the duct itself.

Sorry for the dumb question. How can I measure static pressure. I am a mechanical engineer by education and consider myself as a handyman. So, if you can provide me some details, I will try to do it myself.

[skaranam]

Need the model numbers of the equipment to be sure, but I seriously doubt that cutting a large round duct into one side of the furnace like that is one of the acceptable ways to connect the return to the unit per the installation instructions.

Here are the numbers that I could find

Goodman GMH8 Gas-fired Warm Air Furnace.
CAPF4860C6AA (This model number is printed on the unit). This looks more like a serial number, but there is another serial number next to this number.

I will call installer on Monday to get more information about the unit. Is there any specific information that I should ask for.

[JLADude]

LOL. Sorry. It seems to me a poor but economical design. Based in your discription and pictures, it appears to me the return duct is far too short with few bends. All is good for performance but not for attenuating noise. You would benefit from several properly sized ducts longer in length rather than one big short duct.

[duxinaroe]

Model # suggest a 4or 5 ton, don't know without researching.
but 2000sqft is probably a 5ton. Most manufacturers recommend using both sides of the furnace for return on a five ton for this reason. (or the bottom, not a choice for your application)
looks like the return is 18inch metal on a 20x20 grill.
In my opinion: too small of a grill on too small of a duct on a furnace that should have a return out of both sides of the unit.
adding a 2nd return off the furnace may be the simplist solution.
also is the return in a large area of the house because if you have all the doors closed that return is going to suck harder to get the air back.

good luck
Dux

[skaranam]

Model # suggest a 4or 5 ton, don't know without researching.
but 2000sqft is probably a 5ton. Most manufacturers recommend using both sides of the furnace for return on a five ton for this reason. (or the bottom, not a choice for your application)
looks like the return is 18inch metal on a 20x20 grill.
In my opinion: too small of a grill on too small of a duct on a furnace that should have a return out of both sides of the unit.
adding a 2nd return off the furnace may be the simplist solution.
also is the return in a large area of the house because if you have all the doors closed that return is going to suck harder to get the air back.

good luck
Dux

How easy/difficult is to add a new duct. Can I have a retangular duct in a different location and run it between the wall studs.