Noisy ductwork - what about sound deadening material?

[TheOtherGoose]

The ducts in my house are a symphony of clunks/thunks/pops as the system goes through expansion/contraction.

What about trying to deaden duct noises with heavy, stick-on metal foil like "Dynamat" car noise insulation?

I'm hoping that a "patch" of Dynamat applied to areas that pop/clunk would be enough to quell most of the noise. Like laying your hand on a drumhead, "boom-boom" might become a duller "thump-thump" due to the added mass of the patch.

A quick look at Amazon shows 36 square feet of no-name insulation for about $80.

Does this idea make sense? Thanks for any suggestions you may have.

 

[billconner]

I'm not sure "patches" will do anywhere as much as a full wrap. More mass - weight per square foot - will be better. A peel and stick product. I wondered if there was a spray on coating, perhaps like a pick up truck bed liner.

 

[Evilunclegrimace]

I have tried serveral different brands of of Sound deading mat. The one that I have used the most is Canopus on Amazon at 18 SF for $29.74. As a bonus it is made the the U.S.A.

 

[NS68RT]

If the noise is from expansion and contraction, then something is preventing the duct from moving. If the supply duct is tight against the joists, you can drop it down a little bit. Make sure the duct hangers aren't pinching the duct, you can spread them apart to allow the duct to grow. If there's more than one screw on each hanger, remove one.

Also, check the temperature rise from the return to supply and compare it to the tag on the furnace. If the duct is getting hotter than it should, it will exaggerate the problem.

If the noise is from airflow when the blower starts, you can add stiffeners to the duct. just use some thin metal angle or something to keep the duct from "oil canning".

 

[jjrbus]

I am on a quest to design a quiet box for a generator. One of the things I need to do will be to quiet the skin of an aluminum box, dampening the transmission of noise, I glued plywood to the inside last one I built, which worked well. On the one before that I used a product like Blue Skin for roofs, which I am convinced is the same thing as the expensive car products. Available generic at mobile home suppliers. Another consideration would be self stick roll roofing for low slope roofs. A mass loaded vinyl is sold at the big box stores for walls which might work, but not self adhesive. These all work to dampen sound like the tar applied to the bottom of a kitchen sink. Tar, not sure on that one?? I know they sell duct liner but $$$$$$ and need to dissassemble the ducts.

I am not recommending any of these or guaranteeing they will work, just tossing some ideas out.

 

[readhead]

Is this a new problem? Are there registers that are closed so the air has no where to go?

 

[dcg9381]

I've found that the biggest contributor of HVAC noise is not enough ducting (area) and especially not enough area for return air... Last house we built, I was VERY specific about minimum sizes for return air.
I dunno if this helps.

Around here, HVAC companies spec HVAC tonage, then they send out the crew to run the duct work (no plan). They just kinda "go for it" and we've picked out registers that had bends that were too tight, all sorts of stuff..

Much harder to fix once drywall is up.

 

[Jackfre]

You might be getting oil canning on the Ridgid duct work. If it is plane sheet metal without cross breaks it will oil can. You can sometimes quite them down by taking a punch to the X-center of the duct and denting it.

 

[TheOtherGoose]

Thanks for the suggestions, guys. As this is the first winter in my (new-to-me) house, I'm hearing all kinds of new HVAC noises.

I'm going to see what I can do on the exposed ductwork in the basement. Unfortunately, as the temps drop, the enclosed ducts (over the finished portion of the basement) are also "talking". Does a cylindrical duct expand in a particular direction or just overall?

 

[BD1]

Does it look like the duct work has been crossed braked ? It forms an "X" which is done when light gauge metal is used.

If the duct is flexing when you pushing on it, maybe try screwing light gauge sheetmetal angles to it.

 

[PoorUB]

Thanks for the suggestions, guys. As this is the first winter in my (new-to-me) house, I'm hearing all kinds of new HVAC noises.

I'm going to see what I can do on the exposed ductwork in the basement. Unfortunately, as the temps drop, the enclosed ducts (over the finished portion of the basement) are also "talking". Does a cylindrical duct expand in a particular direction or just overall?

Round duct will creak and pop as it heats up and cools down. I bought a box of flex and cut out a few inches out of the rounds ducts that were making noise and put in flex to give the duct a better chance to move around and it stopped the round duct from making noise.

You can buy round duct canvas connectors that will do the same.

I agree with some of the other posts. If the duct is popping from heat from the furnace it may be hung to rigidly and rehanging it with consideration for movement may help. If it is popping from air pressure in the duct then it is "oil canning" and popping in and out from air pressure. Gluing heavy rubber insulation on the outside of the duct may help, or even like the other post, a sharp rap with a hammer and denting it might stretch the metal a bit and stop the oil canning.

 

[ImmortalSun]

I see it's been a while since you've posted, but I just wanted to ask if anyone's tried using mass loaded vinyl on the outside of the ducts? I’m thinking about wrapping mine to cut down vibration and wondering if it helps more with the low-frequency hum. Also curious if anyone's found a good way to decouple the ducts from the joists to reduce noise transfer.

 

[pcmeiners]

If you go the sound deadening route.......

https://resonixsoundsolutions.com/resources/what-is-the-best-sound-deadening-material-independent-testing-data/?srsltid=AfmBOorLSV-U7HKZMGWdOqQmZKrNVB366p3A85KoKTwsFqjjVaIRojZR

 

[fitter30]

Normally its the large sections of duct that pound like a drum. Top of the duct usually it's tight to the floor joist. Bottom can be stiffen light gauge angle iron or heavy gauge sheet metal angle screwed width wise. With blower on push on center bottom of duct for give.

 

[Milton Shaw]

I remade my inlet duct from metal to duct board and this quietened it enough to be acceptable. Insulation on the inside of the metal duct would have also done this. I went from a straight in metal duct from furnace to filter holder to a 90 degree bend about 3 foot long from filter housing to furnace. All the difference in the world.

 

[karoc]

On your type system we always installed canvas connection between furnace and plenum. This would cut down on noise and provide little give between duct work and equipment

 

[Jackfre]

When we would have the odd oil canning plenum or bit of rectangular duct I’d take a hammer to it at the center point creating the break that eliminates the boom. If exposed. Fitters method is rather more delicate if exposed.

 

[PWC Repair]

Spray foam! I used it on some of my ductwork. It drastically cuts down the tinny sheet metal noise. Not expensive, easy to do..........like spray paint!

https://www.amazon.com/Insulation-Expanding-Sealant-Density-Ceiling/dp/B0D7F5MPFJ/?tag=atomicindus08-20