Duct Liner carcinogenicity and possible alternatives

[andy_eade]

Hi guys,

I'm in the process of designing the HVAC system for my studio and have been doing a lot of research on best practices. As I understand it, the conventional way of thinking for duct work is to use duct board, or duct liner inside your sheet metal ducts as part of your overall sound control strategy (there are numerous other threads here on the forum which explore all of the other best practices such as silencer design, soffiting your duct work etc.). Let me be clear that what I'm talking about here are the Fiberglass-based products that are specifically made for fabricating, or lining HVAC ductwork. It's already a given that lining or building your ductwork with any other kind of Fiberglass material, not rated for such a purpose, is likely hazardous to your health.

In doing this research I've been finding some new information on the safety of using Fiberglass-based insulation products inside duct work over the long term (duct board, duct liner etc.). Opinions still appear to differ, but one always has to question the source of the opinion - NAIMA for example are quick to point out that there's little evidence to support health concerns, while this white paper from the City of Oakland discusses that the International Agency for Research on Cancer (IARC) has classified it as a possible human carcinogen, and there's other research that suggests that it can be a breading ground for mold once dust and moisture get into the ductwork.

So I've been looking at some new products that are not Fiberglass based, and claim to have good acoustic properties while removing the health risks. Most of them appear to be some kind of closed-cell foam. While I can understand how these would improve IAQ (indoor air quality) and reduce the risk of airborn particles and mold etc., I can't see how these could perform well from an acoustical standpoint. Perhaps they help slightly with damping the ductwork, but I would think that closed-cell foam is not absorbtive enough to be effective with airborn sound.

Here are the links to a few of the products I'm talking about:

http://www.armacell.us/products/aparmaf ... exfs-duct/
http://www.armacell.us/products/apspiralflex/
http://www.kflexusa.com/FileUploads/KFA ... screen.pdf

There is another type of product that appears to be a closer competitor from an acoustic perspective, and that is the polyester based liners such as Ductmate linked below. I've yet to hear any real world experience from the sound-attenuation community.

http://ductmate.com/product.aspx?id=146

I'm starting this thread to begin discussions on this topic and would welcome your thoughts and experience. Personally I'm looking to strike the right balance of sound attenuation in my HVAC system (silencer box design, duct design etc) but remove ALL unnecessary risks of adverse health to me my family - especially since I spend about 22 hours of my day here breathing this air!

Be well my noise-making friends!

[andy_eade]

I just found this rather good article that was published in the ASHRAE journal. It's a bit old now (2003) however it does provide a nice comparison of the various products. As I suspected the closed cell foam does not seem to be a good performer for our type of application.

http://www.ehgduct.com/dokumenter/EHGDu ... ustics.pdf

[Soundman2020]

Nice find, Andy. Interesting, and pretty much what I would have guessed. The closed-cell stuff seems reasonable for high frequency fan noise, but doesn't do a lot for the type of low frequency sounds that we need to deal with. For example, one of those products you mentioned has a coefficient of absorption of 0.01 at 125 Hz. Compare that with an inch of OC-701, which is 0.17. The same product shows 0.13 at 250 Hz, vs. 0.33 for OC-701.

You might also find this interesting:

http://www.gearslutz.com/board/bass-tra ... eview.html

Duct liner is designed to be used with high speed air blowing over it. In studio applications, we use it with rather low speed air blowing over it, maybe 5% or 10% of the design limit, max. So I doubt there's going to be much of an issue.


- Stuart -

[andy_eade]

Thanks Stuart. So perhaps I'm going a little overboard in my approach. Since I am adding dampers and zones to each of my studio rooms with the system that feeds also the first floor of my house, I had planned to drop all of the existing main ductwork and line it with duct liner or an equivalent (since this will be common for both studio rooms and the upstairs house). Now I'm wondering if I should not worry about the main duct so much and just focus on the branch ducts into each of the studio zones. Each of the rooms will have silencer boxes on both their supplies and returns.

What do you think?

[Soundman2020]

I had planned to drop all of the existing main ductwork and line it with duct liner or an equivalent (since this will be common for both studio rooms and the upstairs house).

I would still do that, if you can. "Overkill" is often a good thing in studio building! (As long as it is not "ridiculously extreme overkill".) Putting extra duct-liner further back in the system reduces the overall air noise before the air ever gets to your section, which is good, and also reduces it going the other way. The effect might only be one or two dB, but that's still enough to make it worthwhile, in my opinion. Every fraction of a dB you can do will add up to all the other fractions of a dB, and the overall result will be several dB, and that's a good thing! So if you can afford the extra cost and time, then yes, I'd do that.

- Stuart -