A/C duct repair - Help!

Can anyone suggest a good website for info on DIY A/C duct repair? I've searched for a good while and didn't find much detail. Is it something non-professionals are advised to stay away from?

A/C ducts (ironically) but mastic should be used instead. What kind of mastic? I know where the holes are. How much should I use?
Apparently, there are 2 types of ducts: the "box" kind and the kind that's like a coil in a bag. What is the proper name for the coil kind? A section of the coil kind appears crushed in my attic. Does that happen normally over the years? Can I repair that section or must I replace it?
I would appreciate some pointers from a pro. I can't really afford to hire someone right now.
Thanks,
Greg
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Maybe you could tell us what happened to your ducts that they need to be repaired. Are we talking about a 2" hole, or what? Are these rectangular ducts, or round? Do you know how to use tin snips and a rivet gun?
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It is probably best to replace the damaged section.
You should use UL181 approved duct tape [not rubber back duct tape.] You should also use sheet metal collars to join the repaired duct to the new section of duct, and it is advisable to use mechanical restraint [zip ties.] The 'coiled duct in a box / bag' is flexible duct. You can use a sharp large knife to cut the duct, and a diagonal cutter to cut the spring [do not use aviation snips to cut the spring, it will ruin them.] Good luck.
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I've used, and have seen HVAC guys use, Polyken tapes. This one meets the spec you mentioned.
http://covalenceadhesives.com/SearchProductsDetails.aspx?ID
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Yep!
And the stuff comes is wider widths which I have seen on new installations in church buildings.
GREAT STUFF. It can take higher temperatures can can be used with gas dryer vents. Holds as well as screws but doesn't "snag" or catch lint.

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Thanks, everyone, for your suggestions. :-)
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Is it okay to replace a larger flexible A/C duct with one of a smaller diameter (but same length)? I need to replace one (approx. 54" circumference, 14" diameter) and I'd actually like to reroute it around some attic beams, but it's too wide to fit between the beams. Will replacing it with a narrower flex duct increase the pressure and the efficiency? Is this to tricky for a DIY project? What kind of reducing connector would I need? This appears to be the part of the duct that sucks the return air (because I can see the tube shrink a bit when the A/C kicks on.)
The print on the existing duct is hard to read, but it LOOKS like it says:
14 max positive pressure=6" water max negative pressure=1" water max flame spread 25 max smoke developed 60 max velocity= 4000 fpm R 5.6 Perm 0.1 Permaflex M-KE
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Telstra wrote:

And the ZIP file has what virus?
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Duct software a simple program but adequate

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snipped-for-privacy@gmail.com wrote:

Never install a smaller Return air duct! The 14" flex duct could even be too small! http://www.udarrell.com/proper_cfm_btuh_duct_sizing_air_conditioning_systems.html
udarrell
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A very interesting site
wrote:

http://www.udarrell.com/proper_cfm_btuh_duct_sizing_air_conditioning_systems.html
http://www.udarrell.com/principled_adjudication_disputes_administration_justice.html
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On Tue, 24 Jul 2007 01:04:40 -0000, snipped-for-privacy@gmail.com wrote:

Lowes has some of those round insulated ducts in 25 and 50 foot lengths. They are of a much higher R value than your old ones, which means you get more cool air in the summer and warm air in the winter and it saves on your heating bill.
It is a vey easy job to replace the old with the better quality new ones.
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wrote:

Last time I used some 8" it had, I think, R6 stamped on it.

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