Will increasing duct size fix the noise?

14 years ago

I have a zoned Carrier Infinity system. The master bedroom gets a bit loud and I'd like to fix it. The zone is the master suite and I really don't want the bathroom and closet as cold as the bedroom (a/c season) - these vents are damped down which has increased the noise in the bedroom.

The ducts passed a leakage test and I was going to foam them also so I am not terribly worried about leakage. From what I understand, the Infinity should keep pressures reasonable. The fan was set to the slowest option by the tech.

There are 6 inch flex ducts to the 2 4x10 vents. I'd like to know if the noise would likely be better with going to 8 or 9 inch ducts and keeping the 4x10's? Or do I need to increase the register size. Obviously doing both would be best but much easier to just change the duct size. The other option would be to add a register or two but the wife might give me grief with that option.

The system is 3 ton, 2 stage. The master zone is 750 sq feet or so with 6 registers total - probably all 6 inch. The noise is mostly fine on 1st stage - but with the other dampers partly closed, it is noisier than it should be. I am already considering a dumpzone of sorts to help keep the cycle running longer but I don't think that alone will make the noise satisfactory. The dumpzone would be to the open downstairs but I probably wouldn't do a big register or duct - maybe 8 inch with a 4x10. Again the WAF is an issue.

I guess the simple question is the noise usually the duct or the register mostly? I hate the idea of going from a 9 inch duct down to a 4x10 because of all the turbulence right at the register from the reducers. Is there a simple rule of thumb that matches duct size to register size?

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Comments (7)

zl700
14 years ago
A pressure activated motorized bypass, properly adjusted with plenum stats would do the trick.
classicdave
14 years ago
The Carrier Infinity or Bryant Evolution zoning is the best zoning system out there since it is the only modulating zone system for residential applications at this time. Bypass dampers are against the rules with this zone system.

Make sure your air flow is set to comfort not efficiency.
comfort is default the tech should have set this
in installation. -comfort has a slightly less air flow than the efficiency setting.

Next open back your vents in your master bath and master closet. You are not saving any money by dampening the vents. You may actually be hurting the system, if you have extra air think of it as a little dump area that gets cooled for free.

Next
program your main area as a unoccupied area at night. This will help in becoming a dump zone for any excessive air that may be forced to your master bedroom creating noise issue.

Next, 4x10 are these floor vents? floor vents are known to be on the noisy side since they have thin slots. Increasing your duct to these vents will not help with noise issues.
take the vent off and you may see a big difference in noise issues.

If opening up the 2 vents you closed and then creating the main zone as unoccupied in your night time schedule doesn't quiet down the system enough then you may have to add more vents or increase the vents and duct you have.

sorry but that the real stuff. On the bright side you do have a primo zone system!
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zl700
14 years ago
That appears to be their only handicap with that system, its not a true VAV and no bypass options which only means dump zone which is so yesterday.
david_cary
Original Author
14 years ago
So I don't want to open the vents because it is too cold in those areas. I'd rather dump to the downstairs which is possible with an extra duct run. They are ceiling vents.

The flow is set to comfort.

So is the consensus that increasing duct size won't help? If so I'll just add a register
dan_martyn
14 years ago
David,

Classicdave touched on the issue. You have to first determine where the noise is coming from. Typically it is either fan noise being transmitted through the ductwork or the register itself. If you are balancing the system using the register damper, this creates air turbulence through the register, creating noise. As mentioned before, remove the register and see if the noise disapates. If it does, install a manual balancing damper in that branch ductwork, near the main supply trunk. Open the register all the way and damper down using the manual damper you just installed. This should make the noise go away. You can pickup a manual damper at any home improvement/hardware store for a couple of bucks.

Take Care

Dan
david_cary
Original Author
14 years ago
Ok. I am damping at the trunk. The noise is still present with the register off. The noise is not where the flow has been damped but where the flow is maximal. The only question is will I still have noise if I take an 8 and have to reduce it to a 4x10. There is admittedly a lot of air for a 4x10 register.
classicdave
14 years ago
David,
It is odd that someone would put in 10x4's for celling vents.
They should be at least 10x6 vents with 6" or 7" inch flex tied to them.
8" flex normally takes a 12x6 or 14x6 vent.
it looks like you will have to add another vent in that zone that dumps into your downstairs area.

I would not damper anything, you need to add a vent/s or increase the size of the boot/vent and the branch line(flex larger).
if this is a infinity zone control, it is advanced software driven zone control.

how many zones do you have? you may have mentioned but I'm in edit mode and I can't read your first post.

I would let the install contractor know you are not satisfied with the noise issue and that you hope they can correct it. You paid good money and you deserve a good install.

Will increasing duct size fix the noise?

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Will increasing duct size fix the noise?

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