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Keeping Existing Rigid Ductwork Instead of Insulated Flex Duct

post #1 of 5
2/17/13 at 9:39pm
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What are the alternatives to installing insulated flex duct to minimize sound transfer if the basement already has rigid duct work to main floor above and to basement already?

Reasons for potentially keeping the existing rigid include cost of replacing existing ductwork, the decreased airflow/furnace efficiency and mainly health concerns (with a family already prone to severe allergies with dust being a major cause, I am concerned about the amount of dust that would collect in the dips and valleys of flex duct and their more fragile nature not being condusive to cleaning).

Are there insulated wraps that can be placed around rigid ductwork? Would they help some? Would something *like* a mass loaded vinyl be effective? (Although I anticipate much more costly than insulated flex duct, if it would help to alleviate the health issues than the cost would be worth it)
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post #2 of 5
2/18/13 at 12:00am
Best person to talk to would be Ted White at The Soundproofing Company. He should be able to give you the advice and materials you need.
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post #3 of 5
2/18/13 at 5:04am
the concern of metal duct is that it becomes a sound pipe for furnace motor noise into the theater and leaking theater sound out to the rest of the house. They make duct mufflers that fit on round metal duct work to mitigate the problem but again there are nooks and crannies for the dust to collect and I don't think they could be cleaned. I think the secret is to have a really good central air filter on the furnace and there will be minimal dust in the ducts. Not just a thick folded pleat filter but also an electrostatic cleaner. Flex duct is about $1 a foot so I don't buy the cost objection.
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post #4 of 5
2/21/13 at 1:34pm

I've had a parade of contractors come through my home in the last couple of days as I start ramping up to finish the basement.  When I told them of my plans to take out all my hard metal ducts supply the theater room and replace with flexiduct and a separate air exchange/ventilation setup, they all think I'm crazy.  They all say that they have done multiple theater rooms and just put duct liner in there and their clients were happy.  But I think that this has to be done before the ducts are put in.  Retrofitting the ducts seems to be as much work as just replacing them.  And one, I found out, was on a separate HVAC unit so sound transmission through the theater ducts to other areas of the house wouldn't have been a concern.  

 

One person did mention something that sounded interested.  Basically it is a collar that fits at the outlet of the supply before the main trunk duct that is flexible that absorbs any vibration or mechanical noise from the unit before it gets to the ducts.  A similar collar is put in the return just before it gets back to the unit for the same purpose.  He said that existing systems could be retrofit.

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post #5 of 5
2/21/13 at 5:46pm
Doubtful that your existing metal ducts were sized appropriately to install duct liner after the fact. Let alone sized to handle the heat load of an airtight (Soundproofed) theater room with a space heater (Projector)
Edited by BIGmouthinDC - 2/22/13 at 5:14am
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