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Old 04-29-2012, 08:03 PM   #31
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feasability of replacing AC flex ducting by myself?


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Originally Posted by Doc Holliday View Post
I'm in pretty much the same city as Q. I can tell you it's $200-$250 per individual duct run, installed.
so with 13 registers, thats 2,600 - 3,250? thats not terrible i guess. ill have to see what materals cost, this would take me several weekends if i did do it im guessing.

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Old 04-29-2012, 08:50 PM   #32
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feasability of replacing AC flex ducting by myself?


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so with 13 registers, thats 2,600 - 3,250? thats not terrible i guess. ill have to see what materals cost, this would take me several weekends if i did do it im guessing.

Yup. I'm betting you have a few Y's which means that from the plenum itself there is fewer than 13 duct take off's. One big one split into two smaller duct runs and then to the registers.
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Old 04-29-2012, 09:16 PM   #33
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feasability of replacing AC flex ducting by myself?


Here's some info on ductboards. You might be interested in some of their information. The 3rd link is a guide to make ductboards and install flex ducts correctly.

http://www.naima.org/insulation-know...brication.html

http://www.naima.org/insulation-reso...plication.html

http://www.naima.org/publications/AH116.PDF
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Old 04-29-2012, 09:30 PM   #34
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feasability of replacing AC flex ducting by myself?


Oops, I forgot you had a long trunk line so there might actually be 13 take offs from that.
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Old 04-29-2012, 10:18 PM   #35
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feasability of replacing AC flex ducting by myself?


excellent kilosos thanks alot. looking at this pdf about duct board worried me,i dont have anything that could cut grooves like that, i wonder if i couldnt have one fabricated by a professional?
does one typically replace all the plenums when they redo duct work? im guessing it depends on the condition they are in...

btw what are these tools called? maby i could score some on craigslist or something since i just need it for this one project

edit: ah wait i found them, there not too expensive are they... u think i could get away with just one? im thinking a v groove tool? i could make triangle bits as well as squares with one i imagine...

Last edited by Queequeg152; 04-29-2012 at 10:21 PM.
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Old 04-29-2012, 10:38 PM   #36
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feasability of replacing AC flex ducting by myself?


I just did a quick search and found an Amcraft on E-bay for $59.99. Malco has complete kits for well over $300.

Shiplap duct cutting tool.

http://www.amcraftinc.com/amcraft/page1.html

http://www.toolbarn.com/malco-fgvk.html?ref=base
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Old 04-29-2012, 11:04 PM   #37
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feasability of replacing AC flex ducting by myself?


I have gotten away by only using the Red tool and the Blue tool. Cut with the red tool the first 3 cuts and then the last one is blue. Fold , staple and tape. And your done! I don't know if your going to use reducing extended plenum or just one size. But that you would figure out after you do all your manual d calculations.

http://www.amcraftinc.com/amcraft/page3.html

http://www.ebay.com/itm/Amcraft-1084...item35bb23055a

http://www.ebay.com/itm/Amcraft-1102...item519ebabe78

Thats what they look like but you have to buy the right size to cut which ever size ductboard you plan to use.

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Old 05-06-2012, 12:14 AM   #38
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feasability of replacing AC flex ducting by myself?


I am in Houston, replacing my 30 year old flex duct, which is the same mesh kind as shown above. I also needed some ductboard y's. Found a good source for both on Westpark just east of Gessner. R8 flex from Johns Manville. All new fittings as well.
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Old 05-06-2012, 06:25 PM   #39
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feasability of replacing AC flex ducting by myself?


some folks like ductboard, some like flex duct, some like sheet metal. When I re-did my ducts, I went with sheet metal. The cost was not bad and install was easy with a pair of tin snips, self tapping screws, mastic and tape. I can tell you that the electrical bills have been down 25 percent, since the change. Please read up on flex duct installation and read up on ductboard. There are some specific things you have to do for ductboard sealing when you expose the raw fiberglass when cutting. as far as which is best, I will say that there are no issues with steel ducts.. no air contamination (ie fiberglass and mold breeding ground, they are cleanable and the last longer. Just my thoughts and what I have been told.
I also forgot to add that a central line duct, is normally much better, in terms of air flow then a plenum box. I also feel that WYE's, pants WYE's and even Tri-WYE's are better then a plenum box with takeoffs.... again, just my two cents work... remember to watch that static pressure also!!!!!

Last edited by bobinphx; 05-06-2012 at 06:28 PM. Reason: forgot to add
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Old 05-06-2012, 09:11 PM   #40
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Bob, I'd love to have all sheet metal but its a lot of work to piece it together and then insulate it. I am using SM elbows for my corners, flex for the straight runs, pulled tight and supported. This new flex is smooth when its pulled tight. Seems like a good compromise. I thank Fred at askweldin for that tip.

Originally I was just going to replace my old flex duct and Ys with new. Then I got a look inside the plenum. My flex duct is filthy and the duct liner in the plenum is too. Now I'm wondering if I can just remove that duct liner and wrap this plenum from the outside, or whether I have to get a new one to do that. Has anyone ever refurbished an old filthy plenum like this one?
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Old 05-08-2012, 10:57 AM   #41
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feasability of replacing AC flex ducting by myself?


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I am in Houston, replacing my 30 year old flex duct, which is the same mesh kind as shown above. I also needed some ductboard y's. Found a good source for both on Westpark just east of Gessner. R8 flex from Johns Manville. All new fittings as well.
id you dont mind me asking what kind of results did you get? id be super happy with 25% reduction is power usage. it would pay for itself in like 2 years at that rate.
thanks for the tips, ill check those places out when i get that far. ive been stuck on some other issues, so my weekends have been monopolized so far.

bobinphx, RE spiderduct vs trunk and branch setups.
i have been able to read a bit into this manual j book a well as some other pdf's. and from what i can tell my existing duct is definatly a spider type setup. there are atleast 3 triangle plenums that split 9" duct into 2 6's. it dosent seem excessively convoluted as it is setup currently, but do you think it would be worth it to look into building a big trunk duct out of duct board? how do you get that into the attic? id rather not fabricate it inside the attic, yet dragging up like 10 pieces and assembling them in the attic sounds incredibly daunting.

unrelated... but.
im also looking into having more cellulose blown into the attic, as it is currently less than 6 inches in most places. .
this place is hopeless i swear.
how should i go about building a new duct system taking into consideration that id like to blow in another 6" of cellulose? im thinking i would just hang the duct and plenums like 7" off the raters and have it blown in after? i dont see how i could get around in the crawl space with another 6" of cellulose in there.

ALSO, someone left a bunch of foil in the attic... apparently its a "radiant barrier". i for the life of me dont understand how this does anything inside an attic. if anything it should be on the roof actually reflecting sunlight away from the attic. but no, its sitting on top of the insulation? what exactly is it doing? we all know that matter not at absolute zero will emit electromagnetic radiation in what ever wavelength it wants too, but will materials like hot wood really emit enough radiation to necessitate a reflective surface to keep it away from the conditioned space? i seriously doubt it personally... and what little radiated heat it reflects goes where? reflected back into the roof sheathing? what do you guys think i should do with this stuff? take it out? put it back on top of the new duct/cellulose?

honestly my gut tells me, someone was sold a load of BS when this stuff was installed, but i really dont know.

Last edited by Queequeg152; 05-08-2012 at 11:22 AM.
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Old 05-09-2012, 09:26 AM   #42
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feasability of replacing AC flex ducting by myself?


I got a huge reduction from opening up the blower side of the condenser and cleaning that - there was about a 1/2 millimeter layer of matted stuff covering a large part of the condenser grill. So make sure you check that. Who knows who may have run your AC without a filter? That saved me $100/mo in electricity.

I don't have any other results yet as I'm in the middle of revising my design, now that I've seen the plenum. But I'm targeting 20% reduction of cooling bills in the summer. I will also benefit from everything being clean.

Regarding trunk duct: I read bobinphx's message as being against trunk and in favor of Ys like you already have. Pick a duct traveling from your air handler going to a Y or a register and remove it and have a look inside the plenum. If its clean then you can just replace the duct. Your earlier pic of the duct looks clean, a good sign. My mesh is clogged with dust. BTW, triangle is not a plenum, its a distribution box. You can buy those prefab cheaply at the AC place I mentioned. Ask for ductboard triangle box.

I will also blow cellulose into my attic. I have already sealed it and built dams around the bottom of my rafters. But have to redo duct first. I will be lifting it up in the air also. I am adding a bit of floor joists on top of the attic rafters to build a raised floor in a few spaces so I can still get around after the insulation is added. Make sure you use wide strap to hang the duct, and support enough so it doesn't sag. Strap available at AC supply. I will hang the strap with wire and eyehooks screwed into the rafters.

Radiant barrier - I'm installing some because its cheap enough DIY and easy enough to install and it looks good when you sell the house. I dont expect dramatic results from it, but it does have some effect. The idea is that your roof absorbs sun's heat and radiates that into your attic, heating up insulation which then spreads into interior. Barrier will reflect the radiated heat back to the roof. For installation options see attic foil dot com. I'm using their stuff and it works well.

Last edited by rdc; 05-09-2012 at 09:29 AM.
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Old 05-09-2012, 09:37 AM   #43
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Filter on a condenser? Inside is the evaporator coil. On this side of the system, the inside of your home in which enveloped air is being (re) circulated and conditioned, is where a return filter would be associated with the system, not on the outside condenser.

You can also take a hose to your (outside) condenser, rinse off the coils as best you can. Best to turn it off first.

Now you'll be becoming close to having proper cfm across the coils which means close to a properly running system. Close, not perfect, but close(r).
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Old 05-09-2012, 09:51 AM   #44
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Btw RDC, I'd scrap that plenum and get a brand new one. It's actually less headache and much less time consuming and possibley even cheaper. Granted you'd have to install it yourself but it's not a big deal to do so. If you need some tools to do it with, I'm in Houston as well.

I can't charge you as that is against the site rules, to offer my services for monetary gain, but if you do enough of your own work than when I have the time I wouldn't mind assisting.

Btw, that would mean my tools never leave my line of site, you do the work in front of me type deal.

..if you need it.
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Old 05-09-2012, 11:49 AM   #45
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Sorry if I mixed up the terminology - the evaporator coil up in the attic, not the condenser outside (although a lot of water condenses on that evaporator, probably the source of my confusion).
Doc, thanks for your offer, I will PM you.

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