HVAC duct question

**CajunRider** · 04-02-2006, 05:00 AM

I am shopping for flexible HVAC duct. Most flex ducts I've found are rated for R4.2 and 10" H2O positive pressure. I've found some that are rated for R6 and 16" H2O positive pressure at double the normal price. Is the difference worth it? BTW all ducts are in air conditioned space.

Thanks guys.

Sonny Edmonds · 04-02-2006, 08:03 AM

I donno beans about those figures, but....
Wouldn't the first one be kinda "lightweight",
Compared to the second one?
My limited experiance was that the stuff I used for the old house made a world of difference over the crushed, broken, mutilated CARDBOARD tube crap I was replaceing!
Some A'Hole really did a number on those O-riginal ducks that was there. The clown squashed the quack out of them. Jackazz! }>

Rule of thumb, cheap is cheap, and you get what you pay for. Get the heavier stuff and sleep sound. Get the cheap and wake up wondering.
I recon that is yet another reason I sleep well. ;)

:D

[link:home.att.net/~paul.edmonds/|Sonny Edmonds ]
"Precision Firewood Specialist"
God Bless America !
One Nation Under God!
"Lurkimus turdius orifus"

**Jim1142** · 04-02-2006, 03:31 PM

I am a retired sheetmetal worker and contractor and I installed miles of HVAC duct over the years. Is this alumaflex or wire flex? Alumaflex is better and is still lightweight. Wireflex is limp and must be supported a lot more. The most important thing is the instalation. Support the alumaflex every 5 feet and screw and tape the joints with THREE layers of duct tape. If this duct is in a conditioned space ridged sheetmetal pipe will work fine and will be cheaper. It will last 30+ years and is strongest. Again, tape the joints well after screwing them together. Proper sizing of the duct and avoiding 90 degree turns will let the fan do it's job of moving the air well.

**jasfrank** · 04-02-2006, 06:41 PM

Jim; Sorry to be hijacking the forum for a question, but not often one finds someone that has done lots of HVAC work on this forum. I am installing some insulated flex through a vaulted ceiling and was wondering if I dare have foam insulation sprayed around it or will it melt the plastic casing? Or am I pretty much going to have to use glass bats?

**Jim1142** · 04-03-2006, 10:14 AM

will it melt the plastic
>casing? Or am I pretty much going to have to use glass bats?
I do not know. Insulation is not necessary over insulated flex duct. Do a test on it I guess.

**minensoy** · 12-05-2011, 07:14 PM

I've been told from another HVAC repair guy in Savannah, Ga that the solid line, running up from left to right, is the system curve, and that the lines runing down from left to right are the fan curves.

The rated point shows at 635 in all four graphs for the High setting.

What is the CFM for each speed Low, Medium, and High, for 0.20 ESP?

Thanks,
Eric
www.aactionair.net

**jredburn** · 12-09-2011, 09:34 PM

Cajun,
What ever you use DO NOT use Duct Tape. In most States the building code will not allow it. After a few months it will lose its ability to stick to anything and the pressure from the fans will blow it off of the duct and you will be blowing your conditioned air into the crawl space or the attic.
There are a lot of people out there that swear by the stuff but when you have crawled into as many attics as I have and seen ribbons of Duct Tape waving in the breeze you too will become a believer.
The larger the duct diameter, the more conditioned air reaches your living space because of less resistance. The smoother the duct, the same. More corners and sags mean less air to the rooms. Long runs of duct are bad.
When the duct was put in vented attics or crawl spaces, insulation was very important. Now that it goes in conditioned space it is not so important. The cost of higher rated duct may not be offset by the reduction in heating/cooling costs for many years.
Regards
Joe