Foil tape on HVAC ducts
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Hi All,
Just found out that all ductwork (90% round metal) in my new construction high performance residence was ‘sealed’ with foil tape instead of mastic and tape or mastic tape. In addition, it was ‘insulated’ with Reflectix foil bubble wrap (no air gap) so essentially it has no insulation. The house is now sheet rocked and primed. What to do?
Thanks
Andy
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Replies
If it's a temperature rated high quality tape on shiny-new metal ducts it's fine.
If the bubble-pack ducts are all inside of conditioned space rather than up in an unconditioned attic above the insulation that's going to be OK too, though it's a wasted effort. It doesn't take much R to keep ducts from sweating when it's in drier air of conditioned space.
How many wraps?
A single wrap of that stuff is good for about R2, with about half that coming from the low-E exterior surface facing the air. That isn't great, but it's better than nothing. A double wrap is good for about R3, a triple wrap about R4, which isn't terrible.
Per the manufacturer:
"With multiple layers of product and airspaces between each layer, enhanced performance will be gained. If the product is simply “doubled” (with no air space between the layers), a very minimal benefit is obtained, (R-1.1 (per layer) for the Reflective/Double Bubble product)."
and...
"What if there is no air space present on either side of the product?
No Air Space = No Reflective Insulation Benefit (An R-1.1 is provided from the product itself for the Reflective/Double Bubble material.)"
Hi Dana,
I will find out the brand of the tape. But from what I see, it is a thin foil that peels off easily.
The bubble w(c)rap is single layer and wound tight to the duct. No air space, no overlap and taped with more of the same tape. Most of the ducts are in conditioned spaces. At an R value of 1.1, is fair to say that my ducts are essentially not insulated?
What are the Code requirements for HVAC duct sealing? It has to be more than aluminum foil, no? Am especially worried because I am using ducted mini splits which, from what I am reading, are more dependent on properly insulated duct work for efficiency.
Thanks
A
Dana,
I was reading the Code and see that duct tape must have a designation 181B FX or 181 Bm (pressure sealed vs mastic). The tape used on my job has no marking at all.
A
How did your house make it pass the rough inspection phase if the duct work was not insulated or sealed properly? Does your local building department do a mechanical inspection?
No marking at all and "...thin foil that peels off easily..." is a red flag. Not all adhesives are created equal, and you need something that bonds for the duration across time and temperature cycling. The right stuff from any vendor is pretty grippy (marked or not), and while not hard to strip, does not peel easily.
My go-to tape for shiny-clean ducts (not that I'm involved with installing ducts all that often) has been Nashua 324A, which is listed as both UL-181A-P & UL-181B-FX. I'm sure there are several others, but even box stores usually carry Nashua 324A making not very hard to find, and I don't have to read the fine print.
>"At an R value of 1.1, is fair to say that my ducts are essentially not insulated?"
Even at a single-wrap the ducts are insulated at R2, not R1.1. It's R1.1 for every wrap that has NO air on BOTH sides. The outer wrap always has air on the exterior side, giving it about ~R2 performance for that one wrap. Successive wraps only add R1.1 per turn, but the initial wrap is R2-ish unless wrapped in something else. That's "insulated-barely", but still insulated- the first R2 is the most important. Inside of conditioned space even R1.1 is usually enough to prevent condensation on cooling ducts, and the IRC doesn't specify an R value for ducts inside of fully conditioned space.
But R2 is not insulated sufficiently for ducts outside of conditioned space. A quickie reference on what is required for residential HVAC ducts under the IRC lives here:
https://www.masssave.com/-/media/Files/PDFs/Partners/Residential-Duct-System-Requirements.pdf?la=en&hash=210CBFF01AA8A9B3BC935A441881073D63B52FD3
"If following the prescriptive path of the energy code, supply and return ducts located in attics need to be insulated to a minimum of R-8 if they are at least 3 inches in diameter. Ducts smaller than 3 inches located in attics need a minimum of R-6 insulation. Supply and return ducts located in any other unconditioned space, such as a basement or crawlspace outside the building thermal envelope or a garage, need a minimum of R-6 insulation if they are at least 3 inches in diameter, and R-4.2 if they are smaller than that. Be wary of thin duct insulation products like foil-faced bubble wrap that claim to meet these R-values through the use of radiant barriers and air spaces."
They used 3M Venture Tape aluminum Foil 1520CW.
As I mentioned, the drywall is up. The intake and exhaust for my Zehnder are round metal ducts located in exterior walls (exterior cc foam 2.5" and interior cavity cc foam @ 4") with one tight layer of bubble foil 'insulation.' Should we remove drywall and re insulate these ducts?
I worked hard to achieve great efficiency on this house and am extremely frustrated with this low quality installation of one of its most significant components.
Thanks
Hi Dana,
Are you saying that you would use the Nashua 324A to seal new sheet metal ductwork?
Thanks
A
Hi,
That is a very good question.
I assume that the inspector looks at the foil bubble from the outside and assumed it was installed in accordance with manufacturer's instructions (i.e. air spaces).
The 'insulation' covered the foil tape (that has no markings on it) so I guess the inspector assumed the correct tape was used.
AND, I have a general contractor too.. no help there either.
I just learned that it is 3MTM Venture TapeTM Aluminum Foil Tape 1520CW which appears not to be a code compliant tape.
I feel like an idiot for not catching this earlier.
Dont know what to do.
A
No need to feel like an idiot...you are paying professionals that should be responsible for proper supervision and install and relying on your local inspector as extra protection.
How much of the duct work is in conditioned spaced vs unconditioned space such as an attic or basement? A little bit a leakage in the conditioned spaces wouldn't be a huge problem as long as the air is still getting where it needs to go. Exposed ducts in unconditioned spaces could simply be re-insulated and resealed (hopefully at no cost to you).
Has a duct pressure test been done yet? This is mandatory for new installs with any ducts in unconditioned space (at least in my area) and would tell you how bad the system is leaking.
Hi Jon,
90% of the ductwork is within my trusses (conditioned space but no help if air leaks inside the walls).
The 10% of exposed ducts (also within the building envelope) are being sealed using 181BM tape and wrapped in FSK fiberglass instead of the foil bubble nonsense.
The system isn't leaking right now... my concern is 5+ years from now when the stickiness wears off the tape.
The only answer I see (and it is partial since I cannot get EFFECTIVE insulation behind the already installed sheetrock) it to Aeroseal (at no cost to me).
Do you think the lack of insulated ducts will effect the efficiency/operation of my ducted mini split system?
Thanks
A
A proper foil tape is thin metal (very easy to differentiate from any plastic tape), and will stick like crazy. “Stick like crazy” is defined as nearly impossible to get off the duct, and if the tape touches itself while you’re working with it don’t bother trying to separate it and just trash that piece and start over.
I’m thinking you could probably use mastic over the tape to seal everything and be OK, but I’d run that idea by Dana here before you try it.
If you have the option to use aeroseal at no cost to you then that’s what I’d do. There is no reason you should have to worry about future issues caused by problems your contractors caused during construction. If you have the option to put in some extra protection now for free, I say go for it.
I’d be a little concerned about the aeroseal material getting into electrical devices if those have already been installed, but I’d expect the contractor to deal with that. It’s probably an easy matter of just taping over things you don’t want exposed to the sealing agent.
Bill
I do not see how applying Aeroseal today will help if you are correct that the substandard tape is sealing today but will fail at some later date. As I understand it Aeroseal does not coat all of the duct work it only collects at the point on the duct where air is actively leaking out of the duct blocking the flow of air thru the leak. For the Aeroseal to work it must be applied after the tape has failed is that after 1, 5 or 10 years. Do you expect him to do it 3 times?
Did you say 100% of you duct work in inside the conditioned space? In my opinion 5% leakage inside the condition space will be unnoticeably.
If your leaks are outside the conditioned space I say fix it now drywall is cheap very cheap if it has not yet been taped and mudded.
Walta
I agree, based on everything I've seen about Aeroseal it's not going to do anything beneficial in this situation.
Is 3M venture 1520cw substandard tape?
Thanks
A
Andy in post #5 you said the tape is not code compliant. Any product that fails to meet the code requirements is by definition substandard.
Walta
Morning,
The tape is not Code compliant because it has nothing printed on it.
If it were a mastic tape with nothing printed on it, I would irritated because it wasn't Code Compliant but more secure in the long term result. But it isn't. From what I read, this tape is the most basic aluminum foil tape that 'may' be used for HVAC duct sealing. Performance wise, mastic paint or roll is what I understand to be best practices. Performance wise, this tape is barely bare minimum.
A
There’s also a certain amount of guesswork going on here. Does tape and bubble wrap look sketchy? Yes. Would I install that system? No. Will it be a problem? Maybe.
But you don’t know until someone tests the tightness of that ductwork. An energy auditor or possibly even a local utility company would be able to provide that test. Facts are better than opinions. If the tightness test shows leakage rates that are unacceptable, especially if your state or local codes require certain levels of tightness, slam dunk, the installer must re-work the job.
I’ve never seen bubble wrap on ducts before either... I live in upstate NY and I work in the commercial HVAC market so maybe that’s why... but bubble wrap?
You need some facts though, not just opinions.
There should be a duct blast test required at install and again in 5 years. It's the 5 year mark (or 10) that concerns me most. Contractors in my area seem to only be concerned with the 1 year (warranty) results. Houses should be built to last longer than 5-10 years.
I am looking for someone to do not just a duct leakage test but to determine if the small filter will/is cause a drop in pressure. But, I cannot find anyone. have emailed the NCI, still cannot find anyone. All online discussions are great, until help is actually needed in the field and none is available.
I am in 06830 if there is anyone able to help me.
Checking system static pressures is pretty easy.
This cheap digital manometer generally works acceptably.
https://www.amazon.com/Manometer-RISEPRO-Digital-Pressure-Differential/dp/B01680C4C2/ref=sr_1_3?keywords=digital+manometer&qid=1567170468&s=gateway&sr=8-3
Assuming a split forced air system, pull the blower door off and put a small hole in it to get the return side pressure. The supply side is a bit harder, because you want to get between the coil and heat exchanger. Often there is a factory hole for something you can use as drilling in the this area is risky. Insert tube or static pressure probes and check the static pressure.
I've found the hard way that new duct work needs to be wiped clean prior to sealing. Elbow fitting in particular can have a lot of oil still on them. Having to scrub duct prior to sealing makes it pretty grueling work.
Maybe negotiate with the builder that at one year you will have the ducts blasted and if the leakage rate exceeds code, proceed with aeroseal. With all your ducts in the conditioned space, it is unlikely aeroseal is a actually cost effective if you are paying for it yourself.
https://multimedia.3m.com/mws/media/1092763O/3m-venture-tape-aluminum-foil-tape-1520cw-technical-data-sheet.pdf
I agree aeroseal probably won’t do much to seal the ducts themselves, especially if they aren’t yet leaky, but it will help seal any leaks in the building envelope and you gain some efficiency that way. Plus, the OP said the aeroseal application won’t cost him anything so there is really no downside.
I like to use isopropyl alcohol to wipe down any surfaces that I need to tape and have it stay stuck for the long term. The alcohol cleans off any oils and evaporates quickly so you don’t have to wait long before applying tape. The clean surface really helps with adhesion.
Bill
Only the ductwork was areosealed. I have taken great care with my air sealing on the rest of the house, so no worries there.
Maybe you can come work on my project!!!