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Old 04-18-2013, 09:27 AM   #1
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Flex Duct?


The hubs and I are getting quotes to replace our AC system including ductwork. Our existing duct is the flexible crap that was installed in 1988. It's falling apart (holes, tears, collapsing in some areas) and is completely useless.

The quotes we are getting in include R8 flex duct. I'm wary about going with flex duct again but we've been told it's a thousand times more reliable than past products. The price difference between the flex duct and sheet metal is significant.

Is there a reason not to go with the flex duct? Is it really that much better?

Also, something that we didn't ask is how it is installed. Our existing flex duct sits on the floor of the attic - which is a PITA when we put stuff up there and take stuff down (like Christmas stuff). Can the flex duct be mounted on the plywood under the roof or suspended in some manner to keep it out of our way?

Thanks!

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Old 04-18-2013, 09:49 AM   #2
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Flex Duct?


Flexduct can be hung, you just don't want to pinch it so use wide straps to support it. If properly installed there's really nothing wrong with using it.

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Old 04-18-2013, 11:17 AM   #3
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Flex Duct?


not to start the age old flex vs steel... but....

Flex duct has its place in the HVAC world. It works great for short straight runs, such as between a sheetmetal main duct and a register. my opinion only, is that it should not be used for any installation that would need a turn or anyplace it could sag. Further more, flex must be installed (as per MFGR) correctly or you will have significant loss of air flow, which can cause pre-mature failure of your air handler and or compressor (worst case).... so is steel that much better... well... yes..
steel can be cleaned, its stronger and moves air better... but even with steel, you can get a poor installation. I would suggest a bunch of google searches concentrating on "static pressure", "duct sealing" and "duct design". You dont need to become and engineer, but you should know some of the basics so that you can evaluate any contractor. Armed with knowledge you will save money on your heating and cooling bills!!!!!!!!!!!

Here is a great place to start.

http://askweldin.com/Flex.html

as a final thought, in everyday life, which lasts longer.. steel or plastic??? I know that my experiance is that steel lasts longer. The plastic dash of the 1964 car is about gone,, but the steel body is in fine shape...
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Old 04-18-2013, 12:52 PM   #4
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Flex Duct?


Well, if you put it that way... Plastic water bottles will be around for about 6000 years. Steel might last 100 years or so.

I do agree though. I also meant for runs from the main trunk to the registers. What exactly are you thinking about using the flex for?
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Old 04-18-2013, 01:37 PM   #5
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Flex Duct?


LOL 6000 years.... LOL.... not here in the sunny southwest!!! steel yes,, plastic no!!!! LOL

so the bottom line is due to the design and materials used in flex duct, I feel that flex is a bad product. Add to that the industry abuse of the product (bad installation practices) steel is better. I do realize that steel also has issues (bullhead T fittings for example!!) is more expensive, is harder to install etc etc... even with that said, I think steel is superior... just my two cents... and I am still chuckling about 6000 years as that was a great comeback
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Old 04-18-2013, 02:08 PM   #6
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Flex Duct?


I did exaggerate for effect, but it really can take 1000 years. They don't start degrading for about 700 years.
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Old 04-18-2013, 02:36 PM   #7
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Flex Duct?


Hopefully I can explain this without sounding like a complete idiot. Our home is a one-story ranch and the shape of a T. The house used to be a simple 4-walls and roof set up but an addition was done to the back many moons ago. The main truck (sheet metal/steel) runs down the length of the house and I believe there is also a line running to the entrance to the den (the addition). But I could be wrong about the line to the den, it could be flex there too.

The flex duct in there now comes off the main line to the registers (vents, whatever they are called). For the length of the runs, it would go from the main line to the vents, which would be about 9' - 10' long for each room, except for the den where it runs approx. 16 ft.

We are on a budget because we also have to replace our roof this year. We'd like to get both projects done this spring and can't afford to if we go with sheet metal throughout the house.

I'm assuming all the runs are straight, except for the run that goes to our bedroom. For some reason, it comes off the main and twists going through the rafters. The mechanic was scratching his head as to why it was done that way but said he'd do it the proper way. And the trunk/duct is all one size, which I've since learned is a bad thing.

Last edited by kimberland30; 04-18-2013 at 02:41 PM.
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Old 04-18-2013, 02:47 PM   #8
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Flex Duct?


the new flex duct is light years ahead of the old, gray stuff that peels back and simply breaks upon touch after years of being heated up and drying out in the attic heat. new flex duct can handle a hundred years before that happens if at all it ever does.

the aluminum outter seal is the main difference as is the metal coil spring on the inside which stretches the liner and then has the insulation wrapping that and then the outter aluminum liner. aluminum liner rejects heat and the insulation holds heat/cold in, depending if in heating or cooling call. Your old gray stuff you had a mesh that held the insulation in place and that too tears and rips and falls out of the old outter liner.

no worries with flex duct, it's mostly what you see down here in Texas.

Quiet flex will mostly be the brand of flex you get which is made here in Houston, owned by Goodman manufacturing who also is here in Houston, as am I.
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Old 04-18-2013, 07:52 PM   #9
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Flex Duct?


If it's good enough for Texas, it's good enough for VA.
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Old 04-18-2013, 11:38 PM   #10
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Flex Duct?


I know there are pros and cons to both types but having just gone through the same dilemma on flex vs fixed I will tell you this....there are different types of flex duct.

Some is a much higher quality that others. We priced the flex at the big box stores and with a local supplier and we found that the local supplier was not that much more for flex but a huge difference in quality. Just be sure to look at the actual product. You can even do a side by side comparison and you will see what I mean. I'm not an anti big box person - but more lets compare apples to apples

Good luck with your re-ducting...we are in the middle of ours now.

RJ
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Old 04-19-2013, 05:33 PM   #11
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Flex Duct?


RJ: We are going with R8 flex, is that what you ended up getting or is there a higher one than the 8?
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Old 04-19-2013, 08:25 PM   #12
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Flex Duct?


You would pick up 20 to 30 cfm s on each run with hard metal pipe.That is significant.The only down to it is that its must be insulated especially in an attic.
My experience with flex duck systems is that its a lazy man's way of doing things and in my area most flex duct systems also had bad return sizing and installation..I clearly remember when I first got into the business an older fellow told me that one of the most important things to do when installing a furnace system was to make sure the furnace could beathe easy.After hearing that our boss said its even more important that each room breathes easy.Here it is almost 50 years later and I remember that conversation like it was yesterday.
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Old 04-22-2013, 11:45 PM   #13
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Flex Duct?


Quote:
Originally Posted by kimberland30 View Post
RJ: We are going with R8 flex, is that what you ended up getting or is there a higher one than the 8?
Kimberland that is what we have piled up n the back waiting for when I get banished to the attic again. Right now I'm on strike lol. I know its a much higher grade than is available elsewhere.

We have been really lucky with our HVAC folks understanding what we are going through and the need for keeping it cheap. They have been letting us buy the stuff at their prices and they have even gone so far as to lend us tools. They will be doing the important parts but are letting s do some of the other.

Robyn

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