# Flex Duct Vs. Metal/Insulated



## THOMAS RICHARDS

Flex or metal both work
it's just like anything else
it has to be done correctly


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## A.D. Const

montanajim said:


> first of all you should never just upsize a run because it is flex, and second you should never install a forced air system without a load calculation. If you properly size your ductwork, then flex is not an issue, yes they should be ran as straight as possible and pulled tight, but i have personally tested airflow with a flowhood with and without flex using the same heat run for consistency and the air flow remaind the same, flex will increase the static but if properly sized will reduce overall noise of the system. And as for cleaning that is a scam. It is proven that the dirt and debris that are in the duct work under normal operation will not move around after initial start up, also maintaining a clean filter will also eliminate the use of a duct destroying cleaning system. I recommend a proper load calculation, and you can work fine with flex in the system for branch runs, just not the main trunk.


ditto


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## OwenCoffin

*I'd like to hear from those of you who do repair*

My own 25 year old home has flex duct and I just spent 3 days in my crawl space replacing broken pieces. The original installation was poorly done using the wrong tape which had rotted and the whole system was falling apart. Almost none of the heat was going to the house. I had the warmest crawl space in town. The inside plastic had hardened and had turned into a brittle paper like material and shredded. I fixed what I could see and feel but I'm sure I didn't get it all but at least there is no longer any heat loss to the crawl space. Based on what I found there I'm convinced that the rest of it will turn into shredded paper soon so next summer I will rip it all out and replace it with insulated metal.


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## TRANEDOG

thom said:


> Flex must be oversized at least one duct size. Even when doing this the flex duct creates much more resistance. Air flow in a steel duct tends to travel smoothly in a coil-like motion. Air flow in a flex duct tends to tumble, probably because of the rib like intrusion every inch or so. Because of this action, the longer the run the greater the difference in performance with the steel duct being the better performer. This assumes a proper installation.
> 
> Oftentimes flex duct is not properly installed. Joints tend to fail more often, generally an installation error. Bends are especially resistant to air flow in flex.
> 
> It seems that the savings from a faster and cheaper installation don't translate into real money in your pocket. The increased cost of running the system longer more than eats up any installation savings.
> 
> Of course all this ignores duct cleaning which can completely destroy a flex duct.
> 
> In my jurisdiction the problems were great enough that flex duct was outlawed in residential as of 01/01/08.


Bulls*** :no: pretty much 99.9% of "THOM" post...


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