# Isolating sound from Mechanical room



## rjane (Oct 16, 2009)

I am in the process of developing my basement which is below grade in my two storey detached family home. As a result my exterior walls are concrete for the first 8 feet followed by a header space that exists between the silent floor joist system. The basement will consist of four rooms: a bathroom, guest bedroom, home theater room, and office. The guest bedroom, office, and bathroom will not generally be in use or producing noise when my wife and I are trying to enjoy our hometheater set up (our kids are very young and in bed on the 2nd storey by 7 pm). Based on this I believe that the furnace/mechanical room in the basement is our greatest threat to enjoyable sound in the home theater room. For this reason I am planning to take steps to isolate that room rather than isolating the home theater room from the rest of the house. My plan involves roxul safe and sound insulation in the interior walls of the mechanical room which are shared with other space in the basement. On these same interior walls I would hang 5/8 inch drywall a layer of green glue and then 1/2 drywall on the side of the wall that faces into the mechanical room. The other side of the wall which forms the boundary with the bedroom and bathroom would have a single layer of 1/2 drywall. The ceiling joist area leading from the furnace room would also be filled with roxul. The door leading to the furnace room would be a solid core steel exterior grade door with weather stripping (note the furnace and hot water tank all have dedicated combustion air intakes). Lastly the hot and cold air plenums have been framed by bulkheads made with 3/8 OSB that do not touch the metal. I am planning to put a layer of green glue on the OSB prior to hanging 1/2 drywall on the bulkheads to limit sound. With these steps I think I should have relatively isolated the furnace room sound. The only flanking path that will be untouched is the actual hot air duct into the home theater room (it will simply be surrounded by roxul) and the cold air return. Also I cannot fill all of the joist space above the home theater room with roxul because I have already installed non i/c recessed lights which require a 3" space around the light. I figure that insulating the ceiling, but leaving flanking paths where each of the ten lights are is a waster of time and money. The hometheater ceiling is going to be drywall with a popcorn textured ceiling.

Any thoughts, suggestions. Is this overkill or not enough?

PS: I am looking to create an enjoyable place to watch movies, but cannot call myself an audiophile. FYI my system will be a Pioneer VSX-1019 AHK receiver, Energy Take 5.1 classic speakers, PS3 for BD and a 58"-60" plasma yet to be purchased.


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## Ted White (May 4, 2009)

rjane said:


> For this reason I am planning to take steps to isolate that room rather than isolating the home theater room from the rest of the house. My plan involves roxul safe and sound insulation in the interior walls of the mechanical room which are shared with other space in the basement.
> 
> Standard R13 fiberglass may be less expensive and work as well
> 
> ...


I think you can accomplish what you want without exotic materials.


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## rjane (Oct 16, 2009)

Thanks for your response Ted. If I understand the diagram I should surround the duct with fiberglass insulation. I currently have a galvanized boot that angles down aand is framed in by 2x4s and secured tightly so it will not vibrate. The edge that meets the 2x4 box is taped using metalic HVAC tape. Is this okay?

Also I was wondering what your thoughts are on textured pop corn ceilings versus just having smooth finished drywall. Does the texture actually impact sound quality in the room and also reduce sound transmission out of the room ?


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## Ted White (May 4, 2009)

You're welcome, certainly.

Surrounding the flex with insulation, yes. The key is that the insulation + flex duct are within a 4 sided soffit. The ceiling joists are not exposed. Typically the ceiling and wall are double drywalled. Then the soffit built, and itself double drywalled.


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## rjane (Oct 16, 2009)

I was wondering what your thoughts are on textured pop corn ceilings (over drywall) versus just having smooth finished drywall. Does the texture actually impact sound quality in the room and also reduce sound transmission out of the room ?


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## MatrixDweller (Jul 24, 2007)

Popcorn ceiling material is pretty light weight and thin. It could diffuse really high frequencies, but not a whole lot. They're just used for aesthetic purposes. It would have very minimal impact on sound proofing. I prefer the orange peel look myself but didn't do any texture in my HT. Too much skill, that I don't have, involved to make it look great.

You've stated that the mechanical room will be the biggest source of noise pollution into your HT. If you have a noisy furnace, water heater and/or water heater that can be very true, but other periodic noises can trump that occasionally. Impact noise from above and your drain pipes can produce some annoyances if over looked. You can buy preformed pipewrap made from the same sort of material most people use to make absorption panels. You can also get the same stuff to line or surround HVAC ducts (another soundproofing obstacle.

From above my theater room I can hear noise intrusion from where the HVAC vents are positioned. It's minimal but still present when listening at reference levels. It's kind of hard to retro fit the duct work now that the room is all sealed up. Hindsight tells me that I should have resized them, maybe even went rectangular and lined them with something. The hangers they rest on should have some degree of isolation also.

Also if you have to build bulkheads around your ducts and/or pipes leave a little extra space so that you can stuff the cavity with mineral wool and/or surround the ducts in rigid mineral wool.

Another thing that I was lucky to have installed on my furnace return air duct already was a vibration isolator. It basically couples two pipes together by a reinforced vinyl membrane. That stops the ducts vibration from leaving the furnace or entering it.


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## Ted White (May 4, 2009)

I agree with MatrixD. Fiberglass can be used with the same results. Your choice.


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