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Old 06-28-2009, 02:09 PM   #1
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I live in a doublewide trailor, The duct working in the trailor is no good and I want to replace it with flex. I have a brand new already hookedup 3 ton goodman unit that is supplying the original trailor duct work via 2 8" flex pipes coming from a 16". I need advise, I am not new to hard work but I dont know alot about duct work and so on and I would love help in the best way, along with parts list help. Here is a drawing of what I am going to do. I am going to cut new floor vents along the outside walls and make it easier to install and mantain the duct work. any help? Thanks ahead of time.

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Old 06-28-2009, 03:56 PM   #2
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Be better off running a main supply down the middle. And teeing off of it.

18" flex for a 3 ton is better.

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Old 06-28-2009, 04:08 PM   #3
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I am a noobie and dont know what kind of material to use, the 16" down the middle could I get that to work? and coming off from that, how could I off the flex? is there a method? Like I said I am not stuck on one way but I would like to know all options. And would my design work?
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Old 06-28-2009, 04:17 PM   #4
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16" flex is undersized for a 3 ton unit.
So no reason to undersize the new duct. Unless you want poor air flow.

They make wyes that you install.
You run your flex trunk out, and install the wyes where you need them for the branch supplies.

Some companies use tees. Tees are restrictive to air flow.
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Old 06-29-2009, 02:27 AM   #5
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I understand that you would go with it but the in and out "PORTS" off the unit came 16" and 16 pushes 1400 cfm's correct? the 3 ton unit I have only pushes 1200 cfm's. On the wyes coming from the pipe if I run it down the center and branch off how can I get wyes with the right size on both ends? Will these be special order? on the exposed part of the wyes what do I cover them with?
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Old 06-29-2009, 06:36 AM   #6
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No, 16" flex is not good for 1400CFM.

You simply order the wyes the size you need.
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Old 06-29-2009, 04:31 PM   #7
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And try not to have any 180s coming off the Ts, Ys or triboxes, (take these off earlier).
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Old 07-01-2009, 01:23 PM   #8
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thanks everyone but I have a new question for anyone that can help. After thinking and talking to everyone I was told to go with rigid line down the middle and it should be 14x20x40 the home is 48' long. Shouldnt this be reduced to increase flow? Can someone out here help me to get the design down, my local Installer wants to charge me if he has to think he said. Again I am using the same vents locations as above but running down the middle with supply line. Anyone?
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Old 07-01-2009, 01:28 PM   #9
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Yep, it needs to reduce if its over 28' long, or you'll lose too much velocity in the trunk line.
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Old 07-01-2009, 03:35 PM   #10
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what do I need to reduce it down too? any help?
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Old 07-01-2009, 03:48 PM   #11
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That is detemined by the friction rate you need to use. And how many CFMs of air that will be moved through the reduced size of duct.

You contractor that is willing to do it for a fee.
Can design it for you.

You pay a small fee for his knowledge, and his insight since he can see the job.
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Old 07-01-2009, 04:17 PM   #12
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my contractor wants to charge me to design it. there has to be a rule of thumb. This unit puts out 1,200 cfms and I am going to use all of the cfms in the registers. At what foot do I need to reduce it down and what do I reduce it down too?
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Old 07-01-2009, 04:32 PM   #13
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Rules of thumb, are what screws up systems.

I know that he wants to charge you. You statedthat in an earlier post.
Many areas. Contractors won't even do a design for a DIYer.

You have a contractor that is willing to work with you. Pay him his small fee.

Someone else can tell you, I will not.
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Old 07-01-2009, 05:02 PM   #14
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Isnt this what this website is for? I am totally disabled and have to get my brother in laws to install, I cant afford to pay the fee he wants which is $200. I could use that for installing and helping to keep my help helping.
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Old 07-01-2009, 05:10 PM   #15
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Didn't say no one else should help you.
Just said I wouldn't.

200 bucks is cheap.

Your brother in laws shouldn't be charging you to do this.

I know I wouldn't charge a totally disabled brother in law.
I'd help to pay for the material, and design fee's.

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