Recommendations for Crawlspace Ductwork Insulation
I have two issues I am trying to address 1) Animal damage to ductwork and 2) Safest way to insulate ducts, both safest choice of ducting material and insulation. House occupant has asthma.
Animals have been chewing up ductwork in crawl space. Home is in the southeast with heat and humidity although crawl space is sealed and has a dehumidifier. I am adding additional barriers around perimeter to try and stop animals from being able to get in but nature has a way of eventually overcoming the best defenses. So I am considering metal ducts with insulation liner on the interior, but welcome other solutions. My concern with insulation inside the duct is most insulation seems to composed of “fiber”/fiberglass which may not be acceptable for an occupant with asthma. Placing the insulation outside the duct exposes it to animals. I have read of one solution to protect insulation wrapped outside of duct – wrap it with hardware cloth.
Is there a product/solution that is safe for people with asthma ?
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I’m giving your question a bump. While you wait to hear if someone has a specific product recommendation, take a look at this article: Study Details Health Risks of Insulation and Air-Sealing Products. I would also recommend consulting the Living Building Challenge RED LIST—sometimes the process of elimination can lead you to the right product.
To add to this, the Living Building Challenge DECLARE program provides a list of products that disclose most or all of their ingredients, and whether they are red list free or red list compliant (which I believe means that they use red list materials, but in an application that there's not really a better substitute for and/or that ILFI has decided is OK for now). It's a great resource to look for things that are "safe" in some respects, though it can be disheartening to see how many products are not on the OK list, and how pervasive some of the red list materials are.
Note that fiberglass itself is not "red listed" and seems to be a product of some debate -- I've seen people saying it's fine, and people saying it's literally the next asbestos. The reality is likely somewhere in between -- but the idea of putting it *inside* the ducts directly in the airflow stream doesn't excite me, to say the least.
I asked a question a little while ago about duct insulation options, without too many replies. Phenolic foam board is something that exists, though "phenolic foam" is phenol-formaldehyde resin and I'm not sure whether formaldehyde offgassing would be a concern in this application. I wonder if you could do something with round metal duct, insulated on the exterior, and then sheathed in another larger diameter metal duct to keep the animals out of the insulation -- kind of like your hardware cloth idea except with a continuous sheet metal barrier / similar to a double wall chimney.
If the crawlspace is sealed an conditions than you don't need any insulation. The crawlspace is inside your thermal boundry, any losses through the ducting stays inside the house envelope.
I'm in colder climate with pretty hot and humid summers and ducts in conditioned crawlspace are always plain sheet metal. Zero issues with off-gassing and critters will never chew through it.
I agree with Akos that plain metal ductwork is the answer inside conditioned airspace.
As an aside, if you have holes that are big enough that critters are still getting in, it would likely be worth your while to spend some more time on air-sealing and blocking those entrance points. Keeping rodents out should also help with air quality.
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Well it sounds like there is still room for improvement in terms of materials that are truly safe for enclosed spaces where we live.
The crawl space is enclosed in so far as the vapor barrier/lock is not compromised. It has a dehumidifier but it is not air conditioned or temperature controlled. One HVAC specialist said metal ducts are not used anymore because of corrosion. Another feels that a properly insulated metal duct may "sweat" but only on the exterior keeping the interior and liner dry.
I am considering this product as a fiber free, Greenguard Gold certified, and at least appears to have been designed to limit/reduce harmful elements as much as possible. It is a closed cell foam at the end of the day, but so far this is the only thing I have found that might be ok.
Armacell AP Armaflex - it comes with a low voc adhesive spray or low voc factory applied adhesive:
https://www.armacell.us/products/aparmaflexaparmaflexfs-duct/
I spoke to the manufacturer who were forthcoming with information and answered all of my questions. The Microban anti microbial ingredient is a zinc salt. The tricky part with any foam material is the blowing agent used. Azol Dicarbonamide is used which is also used in food of all things or was as a flour bleaching agent or dough conditioner. It is banned as a food additive/treatment in Europe. "The thermal decomposition of azodicarbonamide produces nitrogen, carbon monoxide, carbon dioxide, and ammonia gases, which are trapped in the polymer as bubbles to form a foamed article."
https://en.wikipedia.org/wiki/Azodicarbonamide