HVAC noise at returns

[BlueNote]

I have loud returns and I was hoping somebody could take a look at this and give suggestions on reducing the noise.

Three Story House Approx 2100 sq foot between 1st & 2nd Floor:

Unfinished Basement:
Comfortmaker system. Filter right by blower. Return splits with one going to 1st floor and one going to the second floor. Ductwork going to 1st fl is 16 x 10. Ductwork going to 2nd floor is 12 x 10

1st Floor, Open Floor concept:
Ductwork comes from basement (16 x 10) and stops half way up the wall. Return grill is 16 x 16 and is at the bottom of the wall. This return is loud when it kicks on. Have to turn up volume on TV. I took the grill off and the noise is the same.

2nd Floor:
Ductwork comes from basement (12 x 10) and return is in the master bedroom and is 12 x 12 grill. There is also a return in the loft above the stairs in the ceiling. This return connects to the 12 x 10 ductwork through flexduct in the attic. This return pretty much draws no air. When I take the grill off the return in the master the noise is the same and I can't feel any air coming down when I stick arm up the ductwork. It seems all the air is rushing at the bottom of the opening.


I'm not sure if I don't have enough ductwork? Can I just get a quieter blower? Should the return in the loft be connected to the return in the master? Can I just put filters on the return grills? Anything I can add to the ductwork to soften sound? Even though the basement is unfinshed I use it like it is finished. Should I have a return and registers installed in the basement?

Just ask for any other info. Thanks in advance.

[D-Allen]

Can you find the model # of the furnace?

[BlueNote]

Can you find the model # of the furnace?

EDD4X36FA2

[tedkidd]

How would you like us to take a look? Pictures or a visit?

You posted neither pictures nor location nor details about your system.

Do you have high energy bills? Your house is a system of interconnected systems. Your are indicating an imbalance that, if attacked wrong will increase the imbalance and create others.

Are you hoping for a simple fix, you may be embarking on a Chinese fire drill. The advice you get will only be as good as the details provided.

[BlueNote]

I do not have high enery bills. The system if very effecient. It is just very loud and I'm not sure of the purpose of the return through the attic to the loft.


What info do you need and what would you like pictures of. I even found the drawings page in a pamphlet connected to the furnace. Should I take pictures of that?

[D-Allen]

Your ductwork should be adequate for that unit. As for the noise if you have metal duct it needs isolated. Installing a flex connector would be a start. Maybe insulating the walls inside the blower cabinet with ductboard and first part of return closest to furnace. That return in the master bedroom can be halfway blocked off to pull more air from the loft. Air is like water, it takes the path of least resistance.

[BlueNote]

Thanks DAllen. I will be calling up the HVAC company that services the bldg I work in.

Where should the "flex connector(s)" be switched out at?

[D-Allen]

If there is none, they need installed in the return duct at the furnace. This will isolate vibration noise through the ducts.

[kls-ccc]

I agree with "D" on the flex connector as a start but is the duct a srtiaght shot or is it offset by at least a foot. If it is not offset you have a direct shot from the blower to the grill for noise to travel. Metal duct has a bad habit of carrying and sometimes even amplifying sound, especially line of sight.

[tedkidd]

I do not have high enery bills. The system if very effecient. It is just very loud and I'm not sure of the purpose of the return through the attic to the loft.


What info do you need and what would you like pictures of. I even found the drawings page in a pamphlet connected to the furnace. Should I take pictures of that?

That'd be great, the equipment and the places your ducts run through. An error many make is taking pictures too close. You know the orientation of a close picture, but someone who has never been there doesn't. Keep in mind when looking at a picture you can always zoom in but you can't zoom out.

[BlueNote]

Offset by like a foot and a half.

[D-Allen]

I have other tricks that are easier to just do than try to explain

[mchild]

What tonnage capacity is the cooling system for your home?

From what you say it sounds like most of the return air is being pulled through the first floor return. Air takes the path of least resistance. The longer path up to the second floor (plus possible additional turns and such) makes that a more restrictive path. Plus, since the return grills are not much larger than the ducts attached to them this too can add to the noise.

So, your first conclusion is right. You need larger ducts and possibly a damper that will adjust how much is being pulled through each branch of the return ducting system. Having a static pressure test of your supply and return (if you can get to where the return splits between the first and second floor and test your static pressure on both sides of that split you may well find a big difference and confirmation of this theory) will probably reveal a high return static pressure (and possibly high on the supply side too).

To keep returns from being noisy the air flow through the grills should be about 300 feet per minute. Your system could well have over 700 fpm through the first floor return grill.

[D-Allen]

I don't believe a major overhaul is needed in this case. It's just blower noise traveling through the ductwork. Am I totally misinturpreting the complaint?

[BlueNote]

Correction on the offset by at least a foot. Looking again it's only offset by about 6 inches. Attached are pics for anyone to see....

399: Return grill on 1st floor.
400: Return grill in ceiling in loft connects to metal duct work through flex duct in the attic. Doesn't draw much air.
401: Return grill in master.
403: Return splits. Left side goes up to 1st fl and ductwork stops halfway up the wall. Refer to pic 399......Right side shoots up to master so two return vents going down this one shoot. (400 & 401) 401 pic return has long travel. Approx 8ft in attic then down to basement approx 30ft.
404: "D" The blower is in the compartment below where it says "Comfortmaker". Am I going to want them to install ductboard in that compartment or just to the left?

[BlueNote]

What tonnage capacity is the cooling system for your home?

From what you say it sounds like most of the return air is being pulled through the first floor return. Air takes the path of least resistance. The longer path up to the second floor (plus possible additional turns and such) makes that a more restrictive path. Plus, since the return grills are not much larger than the ducts attached to them this too can add to the noise.

So, your first conclusion is right. You need larger ducts and possibly a damper that will adjust how much is being pulled through each branch of the return ducting system. Having a static pressure test of your supply and return (if you can get to where the return splits between the first and second floor and test your static pressure on both sides of that split you may well find a big difference and confirmation of this theory) will probably reveal a high return static pressure (and possibly high on the supply side too).

To keep returns from being noisy the air flow through the grills should be about 300 feet per minute. Your system could well have over 700 fpm through the first floor return grill.

I appreciate the info. This is all good knowledge for when I call a guy in to help. This is a bit much for my knowledge. I believe when you say it is pulling over 700 fpm because it really pulls air and pushes it out the other end. Like I said before it is very effecient and my bills are cheap.

D - I think it is a combination of both blower noise and air through the ducts. Will be posting pics of drawings soon.

[D-Allen]

Yes. Where that big duct comes down to the furnace is where a flex connector should have been installed. It would also benifit you to have a damper in the duct to the first floor return so it can be adjusted. then you will have more control over pulling air from upstairs by closing the damper starting at 25% closed. too much can starve the furnace.

[BlueNote]

Drawings pictures.
Tried to upload vid of noise but wouldn't take.

[BlueNote]

Yes. Where that big duct comes down to the furnace is where a flex connector should have been installed. It would also benifit you to have a damper in the duct to the first floor return so it can be adjusted. then you will have more control over pulling air from upstairs by closing the damper starting at 25% closed. too much can starve the furnace.

Thanks D. Just so that I am following I should have:
1. Ductboard installed in the bottom two compartments on photo 403. (Even the right side where the blower is?)
2. Flex Connector installed right above where the ductboard will be. (At the connection below where the papers are at in photo 403?)
3. Dampers closed to 25% going to the first floor.

[D-Allen]

Yes, if I remember that particular furnace doesn't have cabinet insulation and without a variable speed motor they tend to be noisey.

[D-Allen]

It doesn't neccessarily have to be ductboard, they can use internal duct insulation.

[BlueNote]

Yes, if I remember that particular furnace doesn't have cabinet insulation and without a variable speed motor they tend to be noisey.

You got that right. It is loud. I'm going to get a guy in here and see what he says first and then make these suggestions. I appreciate the help.

One last question...
I understand the ductboard (insulation to absorb noise from blower) in the bottom two compartments and I understand the damper to the first floor (getting blower to pull more air from second floor returns).

What is the "flex connector" going to do?

[BlueNote]

It doesn't neccessarily have to be ductboard, they can use internal duct insulation.

What is going to absorb the most sound?

[D-Allen]

The flex connector will basically separate the rigidness from the furnace and duct linked to the house in order to ensure no vibration noise into the house duct

[D-Allen]

The internal insulation is what is normally used, it is just easier to install when building the duct