View Full Version : Flex Duct vs Duct Board set up...preformance??
01-24-2006, 11:03 PM
Kinda of a silly newbe..student ???? I've been lead to belive that down here in Florida...or at least my area....Flex duct is the best way to do things...high ceilings..no attic spaces..other reasons. And that Flex is just as good...maybe better than duct board systems.
I for no justafiable reason dont like flex duct systems...too me the flex hoses seem too flimsy...easy to crush by blown in insulation....and the curves seem like they would restrict air flow.....IN my mind...when I see a duct board system..nice stright...ridged....well insulated....it seems better..looks better.
Especialy compared to "spider" setups where from the Pelum they run the flex duct out in all directions like a spiders arms pluged into the pelum....that just looks so mick mouse..hack job to me.
Assuming that the correct size..air flow...is used....what is the view of the wise and all knowing members of this board???
Any way since Im a student and basicly know jack....Im sure Im missing something...and wanted some other views..
Thank you all
01-25-2006, 12:13 AM
I have no problem with the "radial" system where the plenum is centralized in a smaller home and the flex doesn't run more than 20' respectively.
I never use the "spider" system, where it is similar to the "radial system" except the laterals are connected to a distributor or triangle made of duct board and the rooms are supplied by that.
I preffer a trunk line of metal or ductboard to the area that needs flex runs as to keep the flex lenghts to a minimum.
There's nothing wrong with flex as long as the proper calculations are done to provide the needed cfm and velocities. The only crushed flex I've seen is where someone had stepped or crawled over it with no regard. The insulation doesn't have the weight to crush a flex duct as far as I know.
If your run is long, the ductboard is a better choice, using 3-30 degree sections for the 90 degree turns. I always brush on duct sealant on all seams (after staple and tape) that will be impossible to get to after the home is done.
dan sw fl
01-25-2006, 05:09 AM
Originally posted by doglips
I for no justifiable reason dont like flex duct systems...too me the flex hoses seem too flimsy...easy to crush by blown in insulation....and the curves seem like they would restrict air flow..
Trust your eyes...
If it does not "look good" ..
the air flow will not be good
Flex is easily and very frequently subject to
" an abused instllation".
Flexible duct creates
too much static pressure and
reduced air flow
due to poor installations.
Max flexible duct length should be 12 feet with use of an extended plenum made of sheet metal or fiber board.
01-25-2006, 07:10 AM
walterc I belive what I'm calling a spider system is what your calling a "radial" system.....this is one of thouse studet misunderstanding terms mistakes on my part.
01-25-2006, 09:08 AM
Quote;walterc I belive what I'm calling a spider system is what your calling a "radial" system.....this is one of thouse studet misunderstanding terms mistakes on my part.
We called the now "radial" system a "spider" system back in the early 70's (because that's what it looked like), then the experts gave out names to the designs and called it "radial". Still looks like a spider to me. :)
01-25-2006, 09:28 AM
One postive thing about flex duct, you do not run into the taped seams opening up over time, especially in S FLa where the heat in the attic gets hot, and will do a number on the tape adhesive over time when used with duct board. Since there are more seams you are more prone to have duct leaks over time. Flex duct can be formed to take gradual turns, flex board will have sharper turns, guess what that does to the airflow when numerous turns are needed. Since Fla attics are limited in room, duct board may not allow fabrication to take gradual turns.
My only point both have their pros and cons. A good installer will be able to evaluate which to use based on the room availabe, exposure etc!
01-25-2006, 05:22 PM
I hear the negative attitude towards flex all the time. My standing is that the top installers can put together a system using cardboard for ductwork and it will work great but the hacks can screw up no matter what product they use. It just happens that the hacks prefer flex and consequently they give it a bad name. Use top guys and let them choose which product will be best for your particular installation.
01-25-2006, 05:23 PM
I hear the negative attitude towards flex all the time. My standing is that the top installers can put together a system using paper mache for ductwork and it will work great but the hacks can screw up no matter what product they use. It just happens that the hacks prefer flex and consequently they give it a bad name. Use top guys and let them choose which product will be best for your particular installation.
01-25-2006, 05:50 PM
Ductboard???? Doesn't anyone actually use METAL anymore???
That stuff is JUNK, IMO.
01-25-2006, 07:51 PM
I personally have no beef with any of it if it's installed properly. When using ductboard, or foil back insulation, I expect it to be sealed, ironed and stapled. When I see flex I expect it to be short and straight and properly clamped at both ends. As far as metal goes, you still have to seal it, insulate it and be realistic in your expectations of what air can and cannot do well in a duct. The key is, applied and installed properly.
01-25-2006, 09:05 PM
flex is a great product as long as it is installed correctly,as for ductboard its a horrible product and should be done away with. over time becomes a breeding ground for types of fungal growth and breaks down letting fiberglass into the air stream...........its great for the installer though...light weight and can be cut with a cheap steak knife.........as for a trunk system or just a spider system as long as you do the right calculations they both can do the job correctly but thats up to the installer to do his job.........
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