I currently have old, decrepit ducts in the crawlspace, but I got a bid (which I accepted) from an HVAC company to put the furnace up in the attic, as well as new ducts. After reading this forum, it seems that rats like to use flex ducts for their nests. Well, the area I live in has lots of roof rats, and there have been previous infestations in my attic. They are gone, and I have covered all holes I believe, but you never know, so what I was wondering is are there different types of flex ducts available? Can I request that anti-rodent flex ducts be used? Is there anything additional I can do, like for example wrap the ducts in steel wool? Or maybe they sell some kind of steel wool product which can slip over ducts? Thanks.