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post #1 of 14 Old 02-03-2018, 10:50 AM - Thread Starter
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Sound isolation from furnace questions

I have a very loud furnace that is very close to my basement theater setup. There is an open area that leads directly to the tv and when the furnace comes on the audio needs to be turned up quite a bit. I need help on materials I could use to dampen and seal off the sound from the furnace because it is so loud

Thanks in advance


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post #2 of 14 Old 02-03-2018, 10:51 AM
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IMO the best solution would be framing, Roxul (or similar) insulation, drywall and a door.
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post #3 of 14 Old 02-03-2018, 11:01 AM
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I have the same issue. Most furnaces, especially old gas furnaces like my 32 y/o, use a single speed blower. The furnace is either 100% on or completely off. Newer furnaces can (optionally) use a variable speed blower fan, using an ECM module to "pulse" the fan motor (just like what electric RC cars use). The fan doesn't normally blow at 100% speed, so is much quieter. I plan on replacing my old furnace this summer.

You only other option is what eljaycanuck recommends.

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post #4 of 14 Old 02-03-2018, 06:21 PM
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When you say open area are you referring to the open vents required by code for combustible air replacement? If yes I have a solution.
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post #5 of 14 Old 02-04-2018, 03:53 AM
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Most furnaces make a lot more noise than they should. One big culprit is the undamped sheet metal of the furnace and duct work. If you take some time to put damping on these sheet metal parts the results can be amazing. I have glued things on using the expanding foam insulation and have even just stuck expanding foam directly on the sheet metal. for the flat walls of a furnace you can bungy-cord 2ft by 4ft fibrous ceiling panels. go to salvage building supply stores to get it cheap.

The pict shows my current theater projects troublesome ringing duct being controlled by tying sections of carpet on.
this makes the whole house quieter.
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post #6 of 14 Old 02-04-2018, 08:40 AM
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Sound isolation from furnace questions

I agree that dampening is a good start. Maybe large sheets of magnetic sign material that is meant for car doors (think Dynamat). It's removable too. I use a piece of it on a cheap music stand that tends to ring and resonate whenever it's touched, or with loud drums near by.

I
My room, which I've been lazy about finishing, may have a similar situation as yours. I made a built-in rack/ DVD cabinet on the furnace room wall (Still not finished. Doors are planned, as well as complete trim work). I cut through the wall in order to provide access to the wiring from the furnace room. As you would expect, the hole allows the furnace sound come right into the theater room. I need to address this, but it should be easy. I plan on a 2x2 framed box door with insulation within the cavity the 2x2s creates. I will apply foam to the edges of the door as a seal, and use clamps that pull the door tight against the wall. The challenge will be the opening for the cables.

As for the wall framing, I took a budget approach. The wall framing is traditional 2x4. But, it's hanging from the joists with about a 2 inch clearance at the bottom to allow for any floor swelling that may occur due to high clay content here on the Colorado plains. I liberally applied soft caulk to the studs, then added a layer of cheap compressed wood soundboard from Home Depot. Then more caulk, and a final layer of 1/2" drywall. It worked pretty well before I cut the hole in the wall.


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The layer of caulk and soundboard can just be seen above the back of the cabinet. That's the drywall for the under side of the soffet.

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post #7 of 14 Old 02-04-2018, 03:11 PM - Thread Starter
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Quote:
Originally Posted by BIGmouthinDC View Post
When you say open area are you referring to the open vents required by code for combustible air replacement? If yes I have a solution.


It’s more of a crawl space that backs up directly to the furnace area.


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post #8 of 14 Old 02-05-2018, 12:24 PM
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Furnaces can be very loud. They are moving a lot of air very quickly.

The biggest thing that you can do is to put mass between your room and the furnace. Drywall is probably the cheapest material that you can get per pound of mass. I would start there. Build a wall with at least two layers of 5/8" drywall to help block out the noise. Green Glue in between would be a good idea. Any ducts that lead into or out of the furnace will also likely be very loud. Box them in the same way with framing and drywall. Read through the soundproofing thread that is stickeyed to the top of this forum for tons of useful information.
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post #9 of 14 Old 02-06-2018, 02:03 PM
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Quote:
Originally Posted by mizedog View Post
I agree that dampening is a good start. Maybe large sheets of magnetic sign material that is meant for car doors (think Dynamat). It's removable too. I use a piece of it on a cheap music stand that tends to ring and resonate whenever it's touched, or with loud drums near by.

I
My room, which I've been lazy about finishing, may have a similar situation as yours. I made a built-in rack/ DVD cabinet on the furnace room wall (Still not finished. Doors are planned, as well as complete trim work). I cut through the wall in order to provide access to the wiring from the furnace room. As you would expect, the hole allows the furnace sound come right into the theater room. I need to address this, but it should be easy. I plan on a 2x2 framed box door with insulation within the cavity the 2x2s creates. I will apply foam to the edges of the door as a seal, and use clamps that pull the door tight against the wall. The challenge will be the opening for the cables.

As for the wall framing, I took a budget approach. The wall framing is traditional 2x4. But, it's hanging from the joists with about a 2 inch clearance at the bottom to allow for any floor swelling that may occur due to high clay content here on the Colorado plains. I liberally applied soft caulk to the studs, then added a layer of cheap compressed wood soundboard from Home Depot. Then more caulk, and a final layer of 1/2" drywall. It worked pretty well before I cut the hole in the wall.

The layer of caulk and soundboard can just be seen above the back of the cabinet. That's the drywall for the under side of the soffet.

Great minds think alike..ha. Having rear access to the rack is pretty awesome. Mine is closed with a removable rear door made from two layers of 5/8" drywall + GG.






Low height basement in a 100 yr old house...



Lots of work to do yet...

The (new) furnace has a modulating burner and ECM fan, so is very quiet. That said, my larger concern was transmission to the rest of the house. Sound attenuation to and from the furnace was dealt with in a number of ways:

1. Closing in the furnace room with drywall, insulation and a fire rated, weather stripped door.
2. Lining the major air returns with 1" Linacoustic.
3. Duct mufflers installed on any HVAC supply lines heading upstairs.
4. Basement air return dead vent lined with 1" Linacoustic.

Duct mufflers are easy to make and surprisingly effective!



Works great :-)

Last edited by dennwood; 02-06-2018 at 02:10 PM.
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post #10 of 14 Old 02-06-2018, 06:41 PM
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Very cool. Nice setup.
I may end up adding another layer of drywall too.


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post #11 of 14 Old 03-03-2018, 08:41 AM - Thread Starter
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Quote:
Originally Posted by dennwood View Post
Great minds think alike..ha. Having rear access to the rack is pretty awesome. Mine is closed with a removable rear door made from two layers of 5/8" drywall + GG.













Low height basement in a 100 yr old house...







Lots of work to do yet...



The (new) furnace has a modulating burner and ECM fan, so is very quiet. That said, my larger concern was transmission to the rest of the house. Sound attenuation to and from the furnace was dealt with in a number of ways:



1. Closing in the furnace room with drywall, insulation and a fire rated, weather stripped door.

2. Lining the major air returns with 1" Linacoustic.

3. Duct mufflers installed on any HVAC supply lines heading upstairs.

4. Basement air return dead vent lined with 1" Linacoustic.



Duct mufflers are easy to make and surprisingly effective!







Works great :-)


I’m interested in lining vents and installing duct mufflers how exactly do you do it?

Would something like these be worth it?
https://acousticalsolutions.com/prod...noise-control/


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post #12 of 14 Old 03-03-2018, 10:17 PM
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Originally Posted by BIGmouthinDC View Post
When you say open area are you referring to the open vents required by code for combustible air replacement? If yes I have a solution.
I have the setup that you describe. Not trying to high jack the thread, but what would be your solution?
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post #13 of 14 Old 03-04-2018, 05:39 AM
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I have the setup that you describe. Not trying to high jack the thread, but what would be your solution?
First attack the noise at the source. Apply DynaMat Extreme or equivalent cheaper product to the exterior surfaces of the furnace air handler and ductwork. You don't need 100% coverage just large pieces on each sheet metal surface.

Second, create a serpentine pathway lined with sound absorbing material between the furnace and the wall openings, be sure the cross section area exceeds the area of the openings. Mine has two layers of linacoustic on the walls. top and floor and the added walls were made of 3/4 plywood from floor to ceiling.

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post #14 of 14 Old 03-05-2018, 09:01 AM
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I’m interested in lining vents and installing duct mufflers how exactly do you do it?

Would something like these be worth it?
https://acousticalsolutions.com/prod...noise-control/


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Purchase a roll of duct liner..you'll find this product at an HVAC/insulation wholesaler..not the big box stores:



Here's a cut/paste of the duct muffler construction:

Because the basement will have some pretty serious audio, the number one concern is sound traveling through the ducts to other parts of the house, particularly upstairs bedrooms. The strategy has a few layers. First, I'm installing a few duct mufflers, building a few dead vents for supply/return in the basement, and finally lining the main supply and return trunks in the house with 1" acoustic duct liner.

I've tested sound levels at the two upstairs vents, checking them while generating an 84db pink noise signal from my computer speakers in the basement. You can buy duct mufflers, but my situation pretty much requires building them to fit. I designed a strangely similar header and muffler system for my Westfalia van's audio conversion engine, using two different sizes of straight thru stainless mufflers. These are super simple to make, and based on a few online specs, should cut sound levels up to 30 db, in the 1khz range (where voices are centered).

Fantech has some numbers posted for their 2 and 3 foot silencers:



For the 5" duct, I'm using an 8" pipe with 8" to 5" reducers at both ends. This should keep flow restriction very low. Step one is to cut the 8" duct material to size. Using a square and scribe makes for a nicer muffler.



I picked up a duct crimping tool to simplify pipe work, particularly for the mufflers.



This mesh will ensure the duct muffler stays at 5" internally.



The simple calculation of D * 3.14 gives you the wide of mesh to cut. I cut it as below to make it easy to join the mesh to form a 5" tube.



Wrapping in 1" duct liner. The liner is duct rated..the smooth side faces in to prevent loose fibers from circulating. I've also sealed the exposed fiber at both ends with duct sealer. This was a mistake cut on the duct liner..I ended up with a full wrap of two layers which keeps the mesh tube nicely centered in the muffler.



Partially assembled. I wrapped the 8" duct material over the core, and wrestled a bit to pop the pipe seam in place.



Duck sealer! This came from Brock White industrial supply locally. It's water based, duct rated, easy to apply (like thickened latex paint) and quick drying.



Sealing the joints.



Sealing both ends to ensure loose fibers cannot enter the air stream.



They're very fast to construct. The larger one is for the 5" duct heading upstairs, and the 4" ID muffler is to manage the supply (hot) air going to the basement bath. The larger muffler is 48" (as large as I could fit in the space) and the smaller one is about 28". If you basically yell into one, the sound level is reduced by at least 50%...surprisingly effetive. I've measure reference noise levels first, so will update as the HVAC sound project is completed.

With basement pink noise (from my PC speakers) generated at 84 db, I'm measuring 47db on the 2nd floor at vent 1, and 35db at vent 2.





Finally to line ducts, pick up some insulation hangars. There are also versions with perforated bases for attaching with screws. The HVAC/insulation supplier should stock these. You can either build up your own dead vents for intake using these hangars to fasten the liner, use mufflers (they're quick and easy to make) where space is limited, and line your air returns if required. I have two air returns which use closed in basement joists as ducts (very common), so lining these will make a difference. It also cuts air flow, which I addressed by adding a larger air return in the basement via a vertical dead vent. Note that duct liner has a side that faces air flow. Any exposed ends you can coat with duck sealer (or another plenum rated sealant) to prevent loose fibers flowing about.



Hope that helps. A post like this would have saved me a few days of reading and searching :-)

Last edited by dennwood; 03-05-2018 at 09:04 AM.
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