Hope someone can give me some guidance on this one!
I removed the dropped ceiling in part of the downstairs of the 1981
house we just bought in Austin, Tx, and am having to reroute all of
the ducts in the first floor to get them up in the joists. That's not
a problem - I'm just replacing the old gray flex-pipe with new pipe of
the same diameter.
But upon pulling out the old stuff, I saw that ALL of the ductwork -
from the 12" cold air return to the two 10" main feeders from the
attic unit to the duct board distribution triangles and ducts to the
individual vents, had a think black powdery crust lining at least the
bottom surfaces of the ducts and duct board register boxes (boots?).
The crust is dry, dark gray/black, and will flake off if you scrape
it. It's kinda furry, but it's dry. We did 2 mold tests, and they
were not out of the ordinary for this kind of house. It's kinda like
just 30 years of dust and dirt accumulating in the ducts, and crusting
up. Is this normal?
Anyway, to be on the safe side of getting as much crud out of the
system as possible, I decided to replace the 12" cold air return flex
pipe and two 10" main supply ducts from the attic, as well as the duct
board distribution triangles and smaller ducts that I had to change
My question is: when I pull the big ducts off their collars on the
unit in the attic, am I going to find a big, gross mess of crust in
the boxes that connect to the unit in the attic? Will I need to
replace those as well? What about the rest of the unit itself?! And
what is this junk anyway?! I can't take on replacing the attic unit
now - just no time or money left. And it works fine. Am I going to
cause bigger problems by disturbing what is up there?
The thing is, if I'm going to replace these ducts, I have to now
because I have the 1st floor ceilings and the chase all opened up.
After I close them up, I'll never be able to replace them. Is it okay
to put the new ducts on the old plenum and intake at the unit in the
attic, then maybe replace that some other time?
Should I just close it all up and pretend I never opened it and saw
the insides in the first place?
I appreciate any help!
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A 12" diameter Return Air duct is rather small.
What size furnace & Air Conditioner (if you have one) do you have?
I would even go with a 14" Return Air duct for a one & a half ton A/C.
Most home A/Cs are 2-ton or considerably larger.
Get the ducts cleaned.
Here is info on sizing ductwork for efficient operation:
WISDOM PRINCIPLED EMPOWERMENT COMMUNICATIONS -
THE REAL POLITICAL ISSUES & WISDOM Principled PEOPLE EMPOWERMENT
Ductboard & Flex are going to be almost impossible to clean.
Replacement with galvanized sheet metal is the best cure, but is an
Insulate the outside of the metal duct. The fiberglass duct board & the
plastic flex duct are great magnets for dirt, dust, soot, etc...
This is what you're seeing in your existing system.
If you burn a lot of candles, live next to a plowed field or dirt road, have
lots of pets, etc... you have a better idea of what the "stuff" is.
I'd check the sizes as well, as a 12"rnd return & 2-10"rnd supplies only add
up to about 600 cfm SA & 500 RA (@.08/100'),
that's about 1-1/2 ton or 1000 sf in my area...
I'll have to check my Flex Ductulator (Hart & Cooley) but most show about a
60-75% cfm capacity of galv. SM based (TRANE) ductulators.
Really helpful stuff, all - thanks!
The house is about 2000 square feet, 2 story, and the ducts and return
in question are all downstairs serving about 950sq feet. There is also
a return with a 12" flex duct in the ceiling of the upstairs hall
(does that make it a warm air return?) so I guess that one handles the
other 1000 sq feet... Don't know how big the system is, but the
external unit is an Amana RCE48A2D.
I'd love to put in the galvanized sheet metal, but that's beyond my
skill and budget. Sounds like the stuff in the ducts is from years of
accumulation, but I guess I never thought so much would be in there
past the filters! I'll also have to replace the upstairs flex at some
point - it's in the attic and starting to come apart.
But I just took a look at the attachments in the attic; looks like
I'm not going ot replace the big ducts; way huge amounts of pain
there, including having to rebuild the ductboard plenums on both ends
and reattach all teh upstairs stuff, which means I'd have to replace
it all now too, since it's fragile. One of you guys could probably do
the whole thing in a couple hours , but it would kill me!
But all this crud in the system - is it a problem waiting to happen in
the attic unit?
Then he needs his license yanked. Most stuff this bad is someone hiring
someone "on the side" to do it. Usually someone who hasn't a clue as to
This isn't a DIY newsgroup. Are you one of the berated DIYers?
residental A/C Duct trunk lines, in the attic, are (seems to be)
always insulated on the outside. why not on t insulated inside like
comercial buildings?. is it because the the ductwork is above a
suspended cieling and this space is a semi codition space?
Where is participation in this group declared to be by invitation only? And
how do you propose to enforce that?
Look, the only beef I have with this group is that what could be a useful
discussion forum is instead a pointless cesspool where amateurs can freely
enter and they, regardless of whether their questions are reasonable or not,
are routinely advised to "Fuck off and call a tech." Show me a serious
technical discussion in here and I'll show you the thousand hackneyed flame
posts that you had to wade through to find it.
If everyone here agrees that the group should be closed to homeowner
questions, it would be simple enough for the core users to agree on a faq or
charter and post it at regular intervals. Guileless OT posters could then be
referred to the faq and the insults could be saved for the guileful ones.
The current situation leaves the naive outsider who happens upon this group
with the impression that the typical HVAC tech in here is an ill-mannered
supercilious prick who wouldn't light your pipe if his house was on fire. If
that's the result y'aller after, you're doing a great job.
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