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Old 03-20-2017, 08:59 AM   #1
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Doubling Up Insulation


Hi,

I run a small HVAC business out of Westchester, NY. We were wondering if anyone has used regular R8 duct wrap (fiberglass) on top of R8 bubble wrap. Essentially double wrap the duct. Does it make the vents sweat? Does it disrupt the vapor barrier? Are there any major drawbacks or positives to doing this?

Thanks
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Old 03-20-2017, 01:55 PM   #2
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Re: Doubling Up Insulation


We keep our ducts in conditioned spaces, so I wouldn't know how effective it would be.

I assume that you use tape and/or duct seal first. If so, you shouldn't have a problem with it condensating with extra insulation. (I've seen where a joint was missed, and it will blow the insulation right off the duct work with time.)

Cheers!
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Old 03-20-2017, 03:00 PM   #3
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Re: Doubling Up Insulation


It should improve performance in the winter by making the foil warmer (i.e. less potential for condensation) and should be a wash in the summer as you will loose the radiant benefit.

You can wrap the unfaced fiberglass in WRB to prevent wind washing. Be sure all the seams in the foil unit as well as the connections are well sealed.
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Old 03-20-2017, 03:23 PM   #4
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Re: Doubling Up Insulation


Thanks for the input. Yeah, we use mastic and silver tape on most applications. But being where we are the codes change too often and we've been seeing a lot on the end of duct sealants and air leakage so we're trying to get ahead of the game.
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Old 03-20-2017, 03:25 PM   #5
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Re: Doubling Up Insulation


Also, if it helps, 95% of the time we're using 26 gauge sheet metal duct and and either R4 or R8 wrap and R6 bubble wrap.
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Old 03-20-2017, 03:47 PM   #6
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Re: Doubling Up Insulation


Good on you for going above and beyond.
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Old 03-20-2017, 04:22 PM   #7
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Re: Doubling Up Insulation


----------------------------Welcome to the forums!------------------------------

Installing FG over the bubble wrap drops the R-value to R-1+....it relies on the foil to stop radiant heat loss; http://www.greenbuildingadvisor.com/...ed-bubble-wrap

So you would be shooting-yourself-in the-foot; http://www.greenbuildingadvisor.com/...tion-good-idea

Better to double the FG (without compressing too much) and add a plastic (air-sealed) vapor barrier (under 1 perm) on the outside- not a housewrap with 16-58 perms; http://airconceptsllc.com/ac-duct-sweating/

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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
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Old 03-20-2017, 04:31 PM   #8
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Re: Doubling Up Insulation


Quote:
Originally Posted by Gary in WA View Post
----------------------------Welcome to the forums!------------------------------

Installing FG over the bubble wrap drops the R-value to R-1+....it relies on the foil to stop radiant heat loss; http://www.greenbuildingadvisor.com/...ed-bubble-wrap

So you would be shooting-yourself-in the-foot; http://www.greenbuildingadvisor.com/...tion-good-idea

Better to double the FG (without compressing too much) and add a plastic (air-sealed) vapor barrier (under 1 perm) on the outside- not a housewrap with 16-58 perms; http://airconceptsllc.com/ac-duct-sweating/

Gary
Awesome thanks for the info. much appreciated.
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Old 03-20-2017, 08:05 PM   #9
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Re: Doubling Up Insulation


Quote:
Originally Posted by rescomhvac View Post
Hi,

I run a small HVAC business out of Westchester, NY. We were wondering if anyone has used regular R8 duct wrap (fiberglass) on top of R8 bubble wrap. Essentially double wrap the duct. Does it make the vents sweat? Does it disrupt the vapor barrier? Are there any major drawbacks or positives to doing this?

Thanks
first, very sorry you live in one of the most heavily taxed counties in the country. BTW, I voted for Astorino for Governor. just say'n

Now, is your duct work in an attic or a basement? I have wrapped duct in both. I just use one layer of R-8, there is really no need to go overboard with insulation, not to mention the expense. And I have never had a problem with heat runs sweating. Just run your insulation at least 12' down the duct from the plenum. (and wrap the plenum)

you should be fine
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Old 03-21-2017, 05:11 AM   #10
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Re: Doubling Up Insulation


Vents sweat in the summer because they are pulling unconditioned air in from the unconditioned space. Sealing the register box/boot to the ceiling, along with the register, will stop sweating registers.
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Old 03-21-2017, 08:04 AM   #11
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Re: Doubling Up Insulation


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first, very sorry you live in one of the most heavily taxed counties in the country. BTW, I voted for Astorino for Governor. just say'n

Now, is your duct work in an attic or a basement?
Yeah the taxes are terrible, and I can't tell where the money is going haha. But as for the insulation, the ducts can be going in either a basement or attic. The houses vary so much from town to town and street to street here.
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Old 03-24-2017, 09:48 PM   #12
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Re: Doubling Up Insulation


I would think if you really want to be better than average, double the duct insulation and make it a selling point for (you and) the homeowner. Since R-8 uses twice the Btu's of R-16, a simple chart should suffice to show energy/money saved over a given length of time per their location. That is a big step up to savings because R-8 is ridiculously low when attic insulation requirements are at R-30 minimum and beyond. And the heat loss of ceiling plane is +- 70* while in a duct is 90*+ to 20-30* ambient or attic temps for a much greater Delta. A lot of your competition is at the mind-set; "good enough, it meets code"... and use only R-8. Figure; if a HO has the money, or is getting a loan for the money, money or low bid may not be the issue since they probably won't be doing this again at that house anyway- what sets you different from all the others... just my opinion. I'd use one that is looking out for my future interests. Flex duct; long lengths or short ones... another selling point just show the CFM loss on properly installed as well and sloppy installs... and using it rather than smooth pipe in the first place.

Gary
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Old 03-28-2017, 03:50 PM   #13
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Re: Doubling Up Insulation


In our area of the world energy savings are a killer selling point. Con-Ed is the main energy provider by us (gas, power, etc.) and they offer a ton of rebates and discounts on anything "green" to both the HO and ourselves. We've been into the technical science of all this for a while now and the tiniest tweaks and adjustments can save hundreds in a year for the clients and they love to hear that. And, as you said, when the competition decides to fly in and out for the quick buck it makes it easier for us to sell ourselves and our work, the decision to ask about double wrapping being the most recent point we looked into.
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Old 03-28-2017, 04:08 PM   #14
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Re: Doubling Up Insulation


Gary in WA could you email me at (look in my profile for email address), the site won't let me send you a PM because I don't have enough posts. If you could put DIY - Steve Jr as the subject. Thanks

Last edited by beenthere; 03-29-2017 at 05:40 PM. Reason: Removed email address
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Old 03-29-2017, 07:54 AM   #15
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Re: Doubling Up Insulation


To everyone private messaging me, first off, thank you. Secondly, I cannot respond because my account is too new, please feel free to get in touch through our company email posted above with "DIY - Steve Jr" in the heading.
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