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Fiberglass Duct Board Distribution Systems


mgbinspect
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What do YOU think about fiberglass duct board? I have yet to hear an HVAC technician or contractor say anything good about it - declaring it a potential air quality disaster. Yet, an online course through Certainteed, has me rethinking my opinion of the material as maybe the best insulated duct system for a lot of attention worthy reasons:

  • It is uniquely consistent in insulation thickness.

It is easier to form and fit tightly together than any other delivery system, if the installer is meticulous.

It experiences, on average, less heat gain or energy loss than any other duct system. That's BIG when you consider that approximately thirty to forty percent of the inefficiency of an HVAC system can be pinned on the distribution system.

The acoustical properties of fiberglass insulation absorb most noise generated by air handling equipment, air movement and conversation.

In spite of it being fiberglass exposed to the inside duct surface, tests confirm that it is not prone to give up its fiberglass to the air - tested at much higher velocities than it would experience in a heating and air application. The introduction of fiberglass to the interior envelope is "insignificant".

Finally, and most surprising of all, according to Certainteed and contrary to the claims of HVAC guys:

o The thermal properties of fiberglass insulation minimize condensation.

o The inorganic properties do NOT support microbial growth.

I find myself inclined to declare fiberglass insulation duct board the clear champion of all distribution systems. Some of its fine qualities are obvious and indisputable, like its consistent thickness and ability to be formed into a very tight and gap free delivery system. Yet, some of the alleged qualities of this material could very well be unfounded biased sales propaganda.

So, what do you know or understand about fiberglass insulation duct board? Is it a champ or an air quality disaster waiting to happen? Am I brain-washed and in need of enlightenment to the contrary, or does it earn and deserve two big building science thumbs up?

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I don't bother with hearing what venders have to say about duct board because I've had to use it and work with it many times. Issue # 1 is that the seams are taped and they do fail sometimes. The product doesn't do well when exposed to any type of humidity. It's physically weak and easily damaged. The interior material is favored by mold.

The main selling points are that it's more economical (becomes popular when steel prices rise), it's quick to install and can be assembled in place (some locations don't have adequate access to bring in large pieces of prefabbed metal duct).

If it were up to me, I'd never see that product installed as duct again.

Marc

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I don't bother with hearing what vendors have to say about duct board because I've had to use it and work with it many times. Issue # 1 is that the seams are taped and they do fail sometimes. The product doesn't do well when exposed to any type of humidity. It's physically weak and easily damaged. The interior material is favored by mold.

The main selling points are that it's more economical (becomes popular when steel prices rise), it's quick to install and can be assembled in place (some locations don't have adequate access to bring in large pieces of prefabbed metal duct).

If it were up to me, I'd never see that product installed as duct again.

Marc

Marc, I'm honestly curious. Have you actually seen condensation and well established fungal growth on the interior of these distribution systems? When I first heard similar arguments from HVAC guys, it made perfect sense to me fiberglass duct board would be a good environment for fungal growth, but on the other hand, I can see where airflow and the nature of fiberglass could promote evaporation actually preventing condensation and provide very little organic matter for fungi to live on, unless the ducts become quite dirty.

I hope this thread actually casts some light on the system, separating fact from fiction, because I, for one, have no practical experience with the product and wish to formulate an educated opinion about it.

Honestly, I have yet to see a duct system that I really liked. They're all awful. But this one, at least, seems to have potential - especially where energy efficiency is the target.

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Check with the American Lung Association and other air quality folks and you likely will agree with Marc!

I have lots of experience with fiberboard duct material as an inspector and litigant. My life has been threatened by contractors and other inspectors. The local muni inspector was going to "whip my ass" if I did not stop writing poor fiberboard duct installations. Never seen one I liked!

Everything you say is correct and none of the statements are complete.

"It is uniquely consistent in insulation thickness."

so is sheet metal and plastic wrap

"It is easier to form and fit tightly together than any other delivery system, if the installer is meticulous."

only if you like tape and a utility knife.

"It experiences, on average, less heat gain or energy loss than any other duct system. That's BIG when you consider that approximately thirty to forty percent of the inefficiency of an HVAC system can be pinned on the distribution system."

IF you have an average and you agree with premise

"The acoustical properties of fiberglass insulation absorb most noise generated by air handling equipment, air movement and conversation."

I suppose it could be true if the tradesperson did not know about fabric boots, etc...

"In spite of it being fiberglass exposed to the inside duct surface, tests confirm that it is not prone to give up its fiberglass to the air - tested at much higher velocities than it would experience in a heating and air application. The introduction of fiberglass to the interior envelope is "insignificant"."

maybe true if it never moved, never was subjected to impact, never got dirty and you agree a certain amout of fiberglass is good in your indoor air.

Finally, and most surprising of all, according to Certainteed and contrary to the claims of HVAC guys:

o "The thermal properties of fiberglass insulation minimize condensation."

So?

o "The inorganic properties do NOT support microbial growth."

sheet metal does not support mold either.

I can't discuss the details of my legal involvement, but can tell you it concerned a young female atty with MS, a local home inspector, me, local muni inspectors, Ownes Corning, etc. She "we" won.

Use it if you want and when it becomes dust laden with open seams, just replace it!

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Check with the American Lung Association and other air quality folks and you likely will agree with Marc!

I have lots of experience with fiberboard duct material as an inspector and litigant. My life has been threatened by contractors and other inspectors. The local muni inspector was going to "whip my ass" if I did not stop writing poor fiberboard duct installations. Never seen one I liked!

Everythinig you say is correct and none of the statements are complete.

"It is uniquely consistent in insulation thickness."

so is sheet metal and plastic wrap

"It is easier to form and fit tightly together than any other delivery system, if the installer is meticulous."

only if you like tape and a utility knife.

"It experiences, on average, less heat gain or energy loss than any other duct system. That's BIG when you consider that approximately thirty to forty percent of the inefficiency of an HVAC system can be pinned on the distribution system."

IF you have an average and you agree with premise

"The acoustical properties of fiberglass insulation absorb most noise generated by air handling equipment, air movement and conversation."

I suppose it could be true if the tradesperson did not know about fabric boots, etc...

"In spite of it being fiberglass exposed to the inside duct surface, tests confirm that it is not prone to give up its fiberglass to the air - tested at much higher velocities than it would experience in a heating and air application. The introduction of fiberglass to the interior envelope is "insignificant"."

maybe true if it never moved, never was subjected to impact, never got dirty and you agree a certain amount of fiberglass is good in your indoor air.

Finally, and most surprising of all, according to Certainteed and contrary to the claims of HVAC guys:

o "The thermal properties of fiberglass insulation minimize condensation."

So?

o "The inorganic properties do NOT support microbial growth."

sheet metal does not support mold either.

I can't discuss the details of my legal involvement, but can tell you it concerned a young female atty with MS, a local home inspector, me, local muni inspectors, Ownes Corning, etc. She "we" won.

Use it if you want and when it becomes dust laden with open seams, just replace it!

Excellent Les! THIS is what I want and need to understand about this product. Thanks!

Sadly, I do wish I'd run across an HVAC distribution system in a home that I was thrilled with. They seem to typically be a flagrant demonstrations of how little HVAC installers care. I think what I liked the most promising about fiberglass duct board is how easily it goes together and seals up with very little variance in thickness (insulation), unless the installer is a butcher.

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Everything you say is correct and none of the statements are complete.

"It is uniquely consistent in insulation thickness."

so is sheet metal and plastic wrap

The only thing that really bugs me about insulation wrap on ducts is that every time it goes over a corner it is compressed compromising its performance, and it seems like every time there's a transition from hard to flexible duct the junctions have either no, or badly compressed, insulation wrap. I guess I just wish there were more rigid standards regarding duct work, or an idiot proof system.

All of this is an excellent argument for radiant heating.

And split ductless systems, which Kurt raised a while back. I really like split ductless systems.

What's particularly funny - providential, is that I live in a tiny home right now that I originally purchased to be a rental unit. When the economy tanked, I sold my big home I no longer needed because all the kids were grown and gone and moved into this place. IT HAS ELECTRIC BASEBOARD HEAT and a through the wall AC unit. Lol... I've kicked around going to a central system, possibly a split ductless system, but my HVAC buddies tell me the cost of heating and cooling will go up - not down. So I remain on the fence.

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This is one reason I do not like duct board. I found this in a home that was about 10 months old during a 1 year warranty inspection.

Click to Enlarge
tn_2010813181359_IMG_0672.jpg

58.69 KB

So, what exactly are we looking at, Scott? Fungi? Scrap material? I guess, I'm unclear on what surface or material to hone in on. Is the right surface inner duct material that is so dirty it's now gray? Is the darker gray portions of the scrap fungi? Help...

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In the areas where you guys don't like to see duct board, what do the HVAC guys do about the fiberglass sound deadening inside the plenums attached to the furnace? Around here there is nothing done to seal them away from the interior of the ductwork. They are simply cut and glued into place with the edges exposed.

ONE TEAM - ONE FIGHT!!!

Mike

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In the areas where you guys don't like to see duct board, what do the HVAC guys do about the fiberglass sound deadening inside the plenums attached to the furnace? Around here there is nothing done to seal them away from the interior of the ductwork. They are simply cut and glued into place with the edges exposed.

ONE TEAM - ONE FIGHT!!!

Mike

I'm not sure what you are referring to. Maybe it's something not done here. There's the 'accordion like' transition piece between the furnace and the air forward plenum which is used to isolate the blower vibration from the metal plenum. The plenum itself has some insulation on it's interior that's cut from a big roll and glued with a spray adhesive, but that for it's insulating qualities, and, yes, it isn't sealed either. Not that I've noticed any problem with it except for the occasional detachment.

Marc

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This is one reason I do not like duct board. I found this in a home that was about 10 months old during a 1 year warranty inspection.

Click to Enlarge
tn_2010813181359_IMG_0672.jpg

58.69 KB

So, what exactly are we looking at, Scott? Fungi? Scrap material? I guess, I'm unclear on what surface or material to hone in on. Is the right surface inner duct material that is so dirty it's now gray? Is the darker gray portions of the scrap fungi? Help...

Marc, got some of it. Sorry for not being more clear with the picture. This was the return plenum and you are looking in the duct toward the unit. The light colors are just construction dirt(drywall dust). The yellow is pieces of the fiberglass ductboard that were leftover. The entire return was a mess. Some of the ductboard was even torn by I think the alarm company when they routed their lines through the duct.

No mold yet.

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  • 1 month later...

mgbinspect good for you in doing your homework. They were right, ductboard IS the superior product! Its leakage is 1/8 of sealed sheet metal. Most of the problems reported are a function of people who don't know, or care Or Care to know the proper way to fab or SEAL the duct with UL 181 tape ( not duct tape)

Personally we have fabricated millions of Sq Ft of ductboard for commercial work. When you go past the Ft McHenry tunnel on 95 in Baltimore, look off to the right (going south) and see the 8 story 1926, 9 story building that was Montgomery Wards Catalog Bldg (1.2 million SF) The anchor tenant of 500,00 sf of space is the MD Dept of the environment We fabed 250.000 sf of ductboard. The top floor is M&T Bank computer/ check clearing. wwe got fiber glass duct hanging off of 2 110 Ton rooftops with sizes like 52x30. So when I hear that someone can't make an 18x18 plenum stay together on a 2 ton split I find it pretty annoying.

By the way mold doesn't grow on galvanize or board, it grows on dirt regardless of what the duct is made of. Dirt thinks the rough surface of galvanize looks the same as board. It takes liquid water and dirt to grow bugs!

Oh and by the way the IARC people who raised the health issue 20 years ago have reversed themselves and in 2002 said it was OK Check the NAIMA,ORG site.

If you would like to hear what 30 years of fabbing this mat'l has taught me Feel free to email me. You're on the right track but there are places it doesn't belong for practical reasons not technical.

Too much info for this post.

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I'd be more interested in hearing from someone who's on the service side of these systems, after 10, 20, 30 yrs of service. Installers always work with new material.

Marc

It sure would be helpful if someone could simply report, with authority, "Yes, I've seen WICKED mold on the inside surfaces of duct board."

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I'd be more interested in hearing from someone who's on the service side of these systems, after 10, 20, 30 yrs of service. Installers always work with new material.

Marc

It sure would be helpful if someone could simply report, with authority, "Yes, I've seen WICKED mold on the inside surfaces of duct board."

Massive. But only near the air handler where moisture from the evaporator coil kept it constantly wet.

Nothing wrong with ductboard in commercial work where it will happily sit above a drop ceiling undisturbed for decades.

Big problem with ductboard in someone's attic where people will be crawling over it & storing boxes on it.

Commercial & single family buildings are completely unrelated species.

Nothing wrong with ductboard, but putting it in a house is a dumb choice.

- Jim Katen, Oregon

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I'd be more interested in hearing from someone who's on the service side of these systems, after 10, 20, 30 yrs of service. Installers always work with new material.

Marc

It sure would be helpful if someone could simply report, with authority, "Yes, I've seen WICKED mold on the inside surfaces of duct board."

Massive. But only near the air handler where moisture from the evaporator coil kept it constantly wet.

Nothing wrong with ductboard in commercial work where it will happily sit above a drop ceiling undisturbed for decades.

Big problem with ductboard in someone's attic where people will be crawling over it & storing boxes on it.

Commercial & single family buildings are completely unrelated species.

Nothing wrong with ductboard, but putting it in a house is a dumb choice.

- Jim Katen, Oregon

Your post makes me pine for a residential duct system that, at least when newly installed, was so tight and darn near perfectly insulated. [:-weepn]

I just can't run across a duct system that really thrills me. Every other system has a lot of obvious problems regarding both sealing and very inconsistent insulation. They're all just too Dependant upon an installer that cares. (ductboard assembly appears almost idiot-proof. [:-wiltel])

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Ideally, duct systems should be installed within the conditioned space as suggested by 'Hot - Humid Climates' by Joseph Lstiburek. That eliminates much of the problems with them. Don't need to insulate them and small leaks don't translate into loss energy.

Marc

I agree, and am a fan of conditioned crawls, for that very reason, along with the reduced potential for fungal growth.

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Ductboard is not idiot proof. I have installed it and have seen the way that some one miss cuts it when making a fitting and not making sure the joints are tight.

I prefer metal pipe as ductwork. But as you said it depends on the installer.

Idiot proof is an overstatement, for sure. I'm being repetitive in saying this: I suppose the thing I like the most about it is that you can assemble as many feet of it as you wish, and if careful, there will be literally no variation in the insulation thickness or the seal for the entire length of the ductwork. To me, that's worth getting excited about.

I have no problem with metal ductwork at all. It's the insulation systems put around them that I find very inconsistent.

I suppose we're splitting hairs here.

If they could come up with a system of metal and insulation that could be, with care, near perfect as ductboard, I'd be thrilled.

That's all.

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  • 3 months later...

I am seeking information regarding health problems, where to seek diagnoses and treatment, etc.

I developed Parkinson-like movements, seizures, and other ongoing health problems after I breathed fumes from welding and burning excess black Teflon coated ductboard in a barrel inside the building. Actually it was "melted" with a torch when the barrel was full. Ductboard contained an Antimicrobial product that the EPA banned in 2006. EPA will not disclose chemicals used or the health effects fumes from the product might cause.

In 30 weeks they burned 23,360,304 sq ft of galvanized sheet metal and 128 rolls (siez unknown) of ductboard and 850 pounds of galvanized steel listed by weight - not size.

35 men worked double shifts cutting through "sandwiches" made from gluing galvanized sheet metal and ductboard together on an old Vicon Plasma Bed Cutter and welded these, making finished HVAC ductwork.

I hate to sound desparate but I am. My reactions to chemical odors is ruining my life. Thanks in advance! Ann

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