Wire Flex or Aluminum Flex for heater duct

I need to run about 15 feet of ducting to a floor register.
Should I use Wire Flex or Aluminum Flex?
What are the pros and cons of each?
The diameter is 8"
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Both have great resistance to flow of air. Please use galvanized duct pipe, designed for the job.
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Christopher A. Young
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Is it for supply or return?? What is the measured airflow your are looking for?? Are you taking this off an existing system?? Are you going to have to install a new system to handle the additional load and airflow?? Is this new construction?? Is this existing construction?? Is this for an addition on your home?? Have you done the Manual D duct calculations?? Will you be re-balancing the the rest of the air distribution system??
My personal preference is to use tin ductwork.
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The system is existing, it is a forced air furnace.
The ducting is all original, starts at 14" then down to 12" then to 8" to the registers.
There is one leg that was previously modified by the previous owner that I am trying to improve.
In one bedroom they moved the register to another wall in the same room. So what someone did previously, was that they cut the hard rigid line at the original register and added 10 feet of wire flex to the hard line and connected to the new register on the other wall in the same room.
This room / register doesn't get the heat that the other rooms get. I have a Fluke digital multimeter with a IR temperature sensor. After the furnace has been running for about 20 minutes, I will go around and point the temperature probe at the center of the metal registers in all the rooms. I'll read anywhere from 115-125 F but in the room with the modified duct. I read only about 100F. Not sure when I am getting such a temperature drop, the run isn't long nor is the room much different, perhaps the loss is in the wire flex duct material?
The airflow out of this modified leg also seems low but I have no way of measuring it. Would this be due to the resistance of the wire flex?
This modified leg has a slight V shape to it, think a dog leg. The original rigid duct is pretty much inline with the new register, so I am thinking of cutting off the dog leg and adding new duct work direct to the register.
My original post was to ask what material to use. I had two heating contractors out, one wanted to use 6" wire flex the other 8" Aluminum flex. after reading I think neither should be used. And to go with rigid line. I am not cheap. We are only talking about a 15 ft length.
Any ideas?
Thanks

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yup... quit screwing around with it, get a complete Manual J and Manual D calculations done, then have the correct size, super high efficiency, comfort system installed and at the same time, get the entire duct system ripped out and re-installed from scratch, compelete with air balancing. No more problem.
--

Steve @ Noon-Air Heating & A/C

"Stop calling me for freebies Satan,
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rip it all out just because one line was modified incorrectly?
I am just looking to correct the modification to the one line that was poorly installed

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You asked for ideas... that's what you got!
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Tube Audio wrote:

Are you too cheap to use sheet metal?

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Talking about flex that is all I have this days is flex getting it hard once a while would be nice Tony

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You need to use more zip screws.
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Christopher A. Young
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That is all just zip screws and all this time i have being wondering if some one will come out with some contraption that I can get it hard Yhank you Chris you made my day Tony

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