Greetings to everyone,
I have been doing some research on environmentally friendly ductwork
installations and have seen many arguments against using uncoated duct
board. The disadvantages range from a breeding ground for dust mites
and mold to inhalation of micro fiber particles and formaldehyde.
As I have a newborn in my household and my duct board boxes and lined
flex hose are all black on the inside, I am looking to replace the
entire ductwork system. My ductwork is in the attic and will primarily
be used for cooling a small 1300 sq/ft Florida home.
The entire current system is all lined flex hose connected with
triangular duct board junction boxes and terminated with duct board
1. What are my options for replacing the junctions, plenum, and
register boots with non fibrous duct board material?
2. If it's sheet metal, is there a way to insulate them just on the
outside up to R6?
3. My longest current flex hose run is about 11 feet. Is it possible
to design a system using only flex hose that is properly sized?
Plenum =======|Triangle Junction|
5Ft.|| |============|Boot 2|
|| 11 Ft.
Thank you in advance for any suggestions,
Get the ducts cleaned, replace your furnace filter with a new one when
it gets dirty, and don't worry too much. Your baby will do fine. New
are always this way. :)
It's too late. I already ripped everything out. The boots were all
black on the inside anyway, so I am not sure if that can even be
FWIW, if it was my house, I would have left it alone till December. Now,
you are not only without a/c (unless you have a couple of window unit to
use meanwhile), but you get to work in a 130+ deg attic also.
Regardless, to answer your questions- sheet metal all the way is the
best way to go. It can definitely be wrapped outside to R6, though for
your area I would try to get R8 wrap. The easiest, quickest and cheapest
route is a new ductboard plenum and new R8 flex ducts, with new sheet
metal register boxes. You can either get new ductboard triangles, or use
sheet metal Tees or Wyes with the flex. That is not the best way to go,
but around here (San Antonio) that is what about 99% of the houses built
in the last 20+ years have, so while not ideal, it will certainly work
if properly designed. Good luck Larry
Thanks Larry. I am to the point of no return now, so I'll work during
the nights when it's cooler. The flexduct and sheet metal tees will
The only problem with prefabricated metal boxes is that my register
cutouts are about a inch from the joists and the flange will not fit.
Also, the boxes I have seen are lined with the fiberglass exposed
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