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Flexible duct
2

Flexible duct

Flexible duct

(OP)
I've unsuccessfully searched the internet several hours for a supplier of a heavy-duty, 42" diameter, spiral-wire-reinforced, flexible duct for conveying clean ambient air at 5" WC.  Does anyone know where I might find such an animal?

RE: Flexible duct

That does sound rather large.  Probably 20" is the max normally available.  I've spec'd/seen some 42" diam. fabric ducts like DuctSox, but that's probably not what you had in mind.

Could you not employ some smaller parallel paths to accomplish this task?

RE: Flexible duct

(OP)
No, it's an existing duct arrangement used in four different places so it would be a big deal to modify them all - even if I could get the funding approved. The existing 42" flex ducts are almost 30 years old and I can't find any record of who the original suppier was.  I found that www.ducting.com sells flex duct up to 60" diameter, but their's can't take the 5" WC pressure.

RE: Flexible duct

ABC Manufacturer's of Canada makes custom fabric and PVC lined duct for the mining industry.

http://www.abccanada.ca/

I know they will consider specialty runs.

RE: Flexible duct

(OP)
Thanks Chris, ABC says they can make it - I'm waiting for a quote now!

Nice study EmeraldCoastHVACR, that one goes in my references folder.

RE: Flexible duct

Contractors and I always have discussions about length of flex duct and the manner in which it is installed. I detail its use carefully both on drawings and specifications and contractors pooh-pooh the reasons for the details but do it after they have to  remove and replace a couple of pieces.

I have seen the bad results of sloppy flex installations in too many balance reports.

I knew about the high pressure loss, but the paper indicates that my calculations are off by about 10%. All the more reason to limit the use of flex duct.

Excellent paper.

RE: Flexible duct

I'm glad they could help, they're a good bunch down there. I worked on the expansion to their plant a few years back.

RE: Flexible duct

To summarize that paper:

The only time flex came close to galv steel was fully extended and there was considerable loses when at 94% efficiency, which is extremely rare (i've never seen it) in the field.

Expect to see flex duct losses approaching 50% compared to galv metal; in addition, expect to see losses using ductboard with liners more than 33% compared to metal(ASHRAE design manual).

From a techs point of view, my experience shows that ductboard & flex systems lower seer ratings 2 to 3 points with all the deteriorating effect that low-airflow systems give(too numerous to mention here).

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