[jriggy]

Looking to move to bigger and better things in a year or so, so we are working on perfecting this old house... Now up is quieting my HVAC system from excess noise and was looking for a little help… This is for my own sanity as well.

The system is working properly as far as proper amount/number of returns and airflow and all that in this smaller 1800sq ft. 90+ y.o. house so I would like to stick to noise controlling the furnace in its main arteries coming in and out…

I have been replacing some of the air-flow duct lines from the old steel to new insulated flexi-duct, as well as had one return resized and acoustically lined in its interior. This has helped reduce velocity noise in key areas of the house.  Now I would like to take care of the noise we hear coming from the furnace and its main arteries down in the basement. I wish I could have these key existing ducts resized so they could be lined on the interior with the acoustic lining but that would cost thousands.

What I am getting is lots of air-flow noise emanating from the large supplier ducts and maybe the unit itself. this sound encompasses the basement, as well as traveling up the basement stairs and into the kitchen. I am also getting some gas flame noise and some ‘rumble’ vibration noise in the room above the furnace, where my TV/HT second system resides… I believe it is the air handler(maybe?) and the two main ducts that supply the small duct lines that are amplifying the noise..

Here are a few pics of the system:




Below is the duct run below the TV/HT system room




The bit above the actual furnace is called the air-handler, right?

What I am considering doing is to wrap the return duct, air-handler, and the crucial/centrally located supply duct runs in a sound deadening material.

Here are the products I have found so far:
https://acousticalsolutions.com/product/audioseal-duct-pipe-wrap/
And the seemingly more popular Sound Seal B-10 product, that can be acquired from any number of locations—
http://www.soundseal.com/barricade/b-10-lag-qfa-soundproofing-pipe-and-duct-wrap.shtml

Either of these products will cost me anywhere from $575 to $600 + $90 to $100 for shipping. Yikes!

My questions….

 Is there any other way to do this???

Would I want/need the product with the quilted insulation, as linked above (assuming for an even better noise killing effect) or could I get by with just the mass-loaded vinyl without the insulation layer? Which is only $250 a roll..

OR…another possible option— is there any reason I could not use car sound deadening products like Dynamat or the like? This would be a somewhat cheaper option and a smaller and easier product to have shipped, deal with and apply. But will it tame the sound of the system as much and would there be any code violation in wrapping these couple main ducts in the stuff?

Thanks
 jason
 

[Big Red Machine]

I've done this wrong almost every time I have done some sort of room build. But I have mitigated it quite a bit with some simple things you can do. First is break the metal chain. Using the flex duct is correct but the serious HT guys (see AVS Forum HT builds) double it back and forth to slow the air down so the velocity is not "heard".

I found a product like Dynamat years ago that I cannot find again that was adhesive backed and stuck to the duct work. It was one foot wide and came in a roll. Very heavy but very deadening.

Once a room is done if you have not stopped the echo chamber that is the metal ducting from picking up every last vibration and sending it up and down the line you will regret it since it is so much easier to do now.

I was too lazy to dissemble a long duct in the back of my room with 3 trunks coming off of it. I had some adhesive backed wrap for prepping window openings prior to installing windows from HD that I applied to it but that was not enough. It is just a bell waiting to be rung and it carries the sound to parts of the house you don't want it going to. The rest of the ducts passing overhead in the room, the singles, I patched in flexy duct and that worked well for those outlets but not the main trunk piece. If not for the MLV I would have really regretted it. The MLV went under the trunk on the ceiling framing (a bear to do) and was contiguously tied into the MLV coming in from the rest of the ceiling (overlapped and taped with house wrap tape.

The one I should have tackled to be 100%:


Wrapped in MLV:



My furnace is mounted on those cork vibe isolators sold here and there for $2 each. You are doing the right thing by attacking that area as well. I'm happy to talk about it. At least, what I would do, not being an expert and all.

[jriggy]

Thanks BRM,

Did you use any insulation between that duct trunk and the MLV? Looks like some pink showing there in the pic.

I do have some Noico 50mil car sound deadening mats that I recently used around the under/back side of a floor vent box. It is adhesive backed and is sticking fine so far... Would love to just wrap those trunks in this 'car' material and be done with it.

The HVAC industry product is pretty expensive but might perform the best and would look the best, as this is an open area and nothing I will be closing in, so the finished look is important too.

[aldcoll]

You might check the Auto industry as they have many products for sound deadening on the floor boards, doors and roof of cars.  I believe it is self adhesive.   

I have no experience with the products outside of watching some car shows.

Alan

[JLM]

Our house built 12 years ago uses nearly all lined/insulated flexible ductwork.  There's 20 feet of ductwork between my listening room and the furnace and I can barely hear the furnace.  I was in charge of a 3,000 square foot addition to our church prior to that and we used fiberglass ductwork mains and insulated flexible ductwork and could barely hear the furnace. 

But all that flexible ductwork reduces the flow rate significantly, making the furnace fan work harder and making it harder to get uniform heating of the space.  And lining the inside of the ducts (unless fully sealed) can blow off and enter the living space.  Those small particles can embed in the lungs and lead to all kinds of pulmonary disease.

I doubt trying to deaden the outside of the ductwork will help much.

[jriggy]

You might check the Auto industry as they have many products for sound deadening on the floor boards, doors and roof of cars.  I believe it is self adhesive.   

I have no experience with the products outside of watching some car shows.

Alan

Yes, as mentioned, I am considering that as an alternative.

[jriggy]

I doubt trying to deaden the outside of the ductwork will help much.

That goes against the write ups and db numbers for these products, but ok. Ill keep that in mind.

Just a reminder, I am talking about external noise from the duct trunks in the basement, not the noise from individule vents in each room.

[mcgsxr]

Are you building a bulkhead around the trunks at all?

When we finished our basement, I knew I would have a large bulkhead running the full length of the space.

I put Roxul Safe n Sound in the joist bays of the ceiling.  I used the cheaper pink to completely fill the bulkhead.  Before stuffing the bulkhead, if I snapped a finger against the trunk of HVAC it would BONG.  After stuffing (I think I used 4-5 bags of pink for the 20x5x15 inch bulkhead) it makes a dull "tick".

Much better.

But only useful if you are building a bulkhead.  Otherwise the Dynamat type stuff is likely the best bet for the exposed trunks.

Here is a shot when I was around halfway done.  The 2 conduits were installed to make future PJ easy.

[jriggy]

Are you building a bulkhead around the trunks at all?

When we finished our basement, I knew I would have a large bulkhead running the full length of the space.

I put Roxul Safe n Sound in the joist bays of the ceiling.  I used the cheaper pink to completely fill the bulkhead.  Before stuffing the bulkhead, if I snapped a finger against the trunk of HVAC it would BONG.  After stuffing (I think I used 4-5 bags of pink for the 20x5x15 inch bulkhead) it makes a dull "tick".

Much better.

But only useful if you are building a bulkhead.  Otherwise the Dynamat type stuff is likely the best bet for the exposed trunks.

Here is a shot when I was around halfway done.  The 2 conduits were installed to make future PJ easy.

I am not finishing this area of the basement, so am not building a bulkhead.. I have used Roxul Safe and Sound in the joist bays above the most offending duct trunk but I suspect I did not use enough, as it still transmits some through the floor. I like your idea of finish it off with some cheaper insulation.

I am also begingin to believe that the Dynamat or Noico products might dull the echo/ringing to a fair amount.
---------------------------------------------------------------


I could just have a pro here to lower the unit to the low-heat airflow and be done with it! Furnace might stay on longer per cycle but at least I will have some sanity   I did this last season. The unit comes on for longer at a time but is much quieter and seemed to be fine --no ill effects. I don't think the professional would have set it the way if it wasn't ok but ya never know.

Also, I am now considering decoupling the duct trunk from the joists with some isolation hanger devices. But they come in so many shapes and sizes I cant tell yet from looking online which ones would fit best.

Any good source page out there for isolation hangers for ductwork???

[JLM]

My guess is that the fan is oversized to be such a problem (excessive external HVAC noise).  Do you notice that the air comes out of the diffusers very strongly?  I'd find a very knowledgable HVAC contractor to verify and slow down the fan or swap it out for a smaller one.  That should take care of all your problems.

Bryant is a good brand and you have a modern high efficiency furnace.  The ductwork looks very professionally installed (take offs have angled boots, very rare in residential installations).  No doubt the fan is direct drive but may have a variable speed controller (that could be the cause of the high speed/noise, and a relatively simple cure). 

You have isolation joints, so with the right size/speed of fan you should be good. 

[ArthurDent]

Tricky question, and as with most things can get fairly involved. Appears most of your sound issue is fan & velocity related. The fan section of your furnace is the 'air handler'. In general your return ducts shouldn't be an issue unless it's from vibration. Return air is usually gravity feed, or induction in residential settings. Does your system have dampers on/in the feeders, or simply face dampers at the grilles or registers ?   

  vs 

The insulating materials you & others have noted should help quite a bit, but getting the system working as efficiently as possible will do a lot too, and save money.

As such the fan wouldn't/shouldn't be oversized, depends on how the system was designed. If you've got a good HVAC contractor talk it over with him, see what he suggests. Ask if he does "air balancing", if not can he recommend someone, and if he thinks it might help. Given the size of your house it shouldn't be terribly expensive to have it checked. If the system can be balanced to where the proper amount of air is going to the desired locations, presuming the basic duct sizing is correct, that should take care of a good bit of the velocity noise.

To the unit noise itself, well, it's a piece of mechanical equipment, and like most is going to make some noise. The insulation should help, simply a question of how much. Pretty sure we've got some HVAC pros here, maybe one of them will see the thread & chime in. Good luck on finding the solution that works for you. 

[jriggy]

Thanks guys.

I adhered the Noico sheets onto the one trunk under the TV/HT system and it did lessen the gas flame 'rumble.' Next I will try to decouple/isolate that trunk from those same floor joists.

I also plan to get the temperature rise checked to see if I can lower the airflow without any issues... I read how to do this in the manual but I bet more than one of you on here would tel me to leave it to the pros    If  Just cut the airflow down either of the options, 7, 10 or 18 % and Im sure I would no longer be bothered by the noise.

Jason