# HVAC Question re: Duct Mastic
**URL:** https://boards.straightdope.com/t/hvac-question-re-duct-mastic/385811
**Category:** Factual Questions
**Created:** [December 28, 2006, 12:09am UTC](https://boards.straightdope.com/t/hvac-question-re-duct-mastic/385811 "2006-12-28T00:09:16Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Enright3](https://boards.straightdope.com/u/Enright3)
#### Post date: [December 28, 2006, 12:09am UTC](https://boards.straightdope.com/t/hvac-question-re-duct-mastic/385811/1 "2006-12-28T00:09:16Z")
OK, so I had an energy audit. Some of the duct work coming out of my heater needs mastic applied to the joints?
Are their alternatives? I have duct tape, I have insulatated duct tape (looks like foil with sticky insulation on it. I have Great Stuff crack sealer.
While I have this thread open, I’m looking for good information via knowledgeable (experienced) people or informative websites on making my home more energy efficient. I’ve added weather stripping around the attic door, changed my old thermostat to a programmable one.
E3
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### Author:  [@Enright3](https://boards.straightdope.com/u/Enright3)
#### Post date: [December 28, 2006, 12:20am UTC](https://boards.straightdope.com/t/hvac-question-re-duct-mastic/385811/2 "2006-12-28T00:20:41Z")
Ahh, I found my fist answer right [on the DIY Network](http://www.diynetwork.com/diy/home_building/article/0,2085,DIY_13953_2595827,00.html)
Don’t Use Duct Tape!
> [@](#):
>
> If ducts aren’t well sealed (that is, that a special sealant – not duct tape! – is used to seal all joints and seams), air can leak from the supply ductwork before it gets to the rooms.
What products are out there to unsulate the ducts afterwords?
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### Author:  [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)
#### Post date: [December 28, 2006, 12:42am UTC](https://boards.straightdope.com/t/hvac-question-re-duct-mastic/385811/3 "2006-12-28T00:42:28Z")
The product is called “duct insulation”. According to one EPA chart, in your region (assuming you really are in GA), unconditioned basements and crawl space ducts need a maximum of R-4, and unconditioned attics need R-4 to R-8. The insulation itself takes several forms, including rigid board, faced fiberglass, Reflectix™, and spray-on foam.
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### Author:  [@ftg](https://boards.straightdope.com/u/ftg)
#### Post date: [December 28, 2006, 2:55am UTC](https://boards.straightdope.com/t/hvac-question-re-duct-mastic/385811/4 "2006-12-28T02:55:30Z")
I have a family member that was in the energy audit business for a while. Mastic is indeed the only useful method for sealing ducts. Not just at joins but also along the seam.
BTW: A typical big box hardware store should sell two types of foil tape. The cheap kind and the real stuff. The latter will have red printing on it indicating that it meets US govt. standards. (Ergo, the cheap stuff shouldn’t be used on ducts.) Of course “duct tape” is an even worse idea on ducts. Basically the problem with even the best foil tape is that the air flow will eventually work its way around it.
After applying the mastic (wear your worse clothes and plan on having mastic blobs stuck to you for a while), then you can add insulation. Duct insulation does nada for sealing leaks.
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### Author:  [@Ring](https://boards.straightdope.com/u/Ring)
#### Post date: [December 28, 2006, 5:09am UTC](https://boards.straightdope.com/t/hvac-question-re-duct-mastic/385811/5 "2006-12-28T05:09:50Z")
[QUOTE=danceswithcats]
The product is called “duct insulation”. According to one EPA chart, in your region (assuming you really are in GA), unconditioned basements and crawl space ducts need a maximum of R-4, and unconditioned attics need R-4 to R-8. The insulation itself takes several forms, including rigid board, faced fiberglass, Reflectix™, and spray-on foam.
[/QUOTE]
In my nearby area, R-30 insulation is recommended for the attic. Why wouldn’t the same rating be correct for the duct insulation?
PS: I don’t know how to punctuate. Should there be a comma after “my.”
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### Author:  [@Enright3](https://boards.straightdope.com/u/Enright3)
#### Post date: [December 28, 2006, 5:59am UTC](https://boards.straightdope.com/t/hvac-question-re-duct-mastic/385811/6 "2006-12-28T05:59:49Z")
[QUOTE=Enright3]
What products are out there to unsulate the ducts afterwords?
[/QUOTE]
~sigh~ of course I meant Insulate, not Unsulate. Give me a break as I have a bandaid on my finger.
E3