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Questions & answers about fiberglass HVAC duct damage as a source of airborne fiberglass fragments:

Frequently asked questions about fiberglass in or on ductwork: fiber shedding, indoor air quality hazards, proper & improper installation, damaged HVAC air ducts.

This article series provides information about fiberglass hazards in heating and air conditioning ductwork in residential and light-commercial buildings.

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Recognizing Fiberglass Duct Insulation

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Recently-posted questions & answers about fiberglass HVAC ducts or "air ducts": installation, troubleshooting, damage, fiberglass shedding and other topics.

On 2017-04-03 20:06:06.346030 by (mod) re: what color is the fiberglass in HVAC ducts?


Fiberglass insulation is sold in various colors, usually specific to a manufacturer. It doesn't have to be yellow.

But you should not be seeing insulation blowing into your occupied space from the HVAC system. If that's happening fiberglass somewhere in the air path is improperly-installed, damaged, or otherwise defective.

On 2017-04-03 20:02:55.550873 by Berenice

The insulation that is coming in through HVAC system in new mobile home is a darker, almost purple color. Should it be yellow, like the insulation under trailer? Or does it get dirty and turn color?

On 2016-11-27 22:56:07.987170 by (mod) re: how to remove fiberglass from vents and HVAC ducts - blamed on health issues


You'd have to replace the ductwork. Before going to that expense I'd want to be darn sure that the ducts were the problem.

On 2016-11-26 23:36:40.035762 by Coco

Hi, please can you tell us how to remove fiber glass/glass wool from vents and hrvc ducts and from the house as all in house also and causing health issues. Thank you.

On 2016-10-31 23:49:40.989305 by (mod) re: is it possible to pull remove the fiberglass and put ductwork back up.


Please use the page top or bottom CONTACT link to send me photos of the duct exterior and interior and I'll comment further. I suspect I'll end up agreeing that duct replacement will be less costly.

You do not want un-insulated ductwork nor ductwork with shredded fiberglass in the air path. While large fiberglass fragments are not likely to be highly harmful, shredding as you describe the operation is likely to also create small fragments that can be harmful - a health hazard; furthermore, doing nothing or doing the wrong thing at this point risks both health hazards for building occupants and a liability for you as a landlord.

Meanwhile, DO NOT run the air handler / blower. You risk blowing more fiberglass around the home and thus having to do additional cleaning.

On 2016-10-31 22:44:46.748073 by Bob Beltran

I wonder if it's possible to pull out the damaged main and remove the fiberglass and put it back up. Seems less expensive than replacement, although the stripped ductwork would have no insulation. It's in the unheated basement. I've taken the end off the main and found the fiberglass is torn to pieces. Just hanging down in strips, rolled or wadded up in places. As I said, one section is almost completely blocked by it. Not sure how to post photos here.

On 2016-10-31 22:29:48.647556 by (mod) re: fiberglass ductwork damaged by "duct cleaning" company

Oh for heavens' sake! Sending a mechanical thrashing type duct cleaning device inside of fiberglass-lined HVAC ducts is likely to cut, shred, and damage the duct insulation. Fiberglass duct liner used inside of ducts is usually coated with a surface sealant to retard fiber release as well as to improve moisture and dirt resistance. Now I suspect the insulation is damaged, creating several issues: fiberglass release, faster soiling, increased risk of moisture retention, possible mold contamination.

It *might* be possible and feasible to have a specialist contractor apply a spray sealant to the entire duct interior. I would first inspect the conditions inside the ductwork by making appropriate openings at representative locations so that you can see just how much damage and how extensive the damage is. Your spray sealant contractor should also look at those conditions and should tell you if she expects the result to be acceptable (smooth-surfaced and sealed) or not before proceeding lest we throw good money after bad.

If that approach won't or doesn't work acceptably I'm afraid replacement of the damaged duct sections need replacement. I'm also afraid that faced with that cost your original cleaning contractor is going to run for the hills.

On 2016-10-31 22:23:07.039763 by Bob Beltran - When I turned the system ... gobs of fiberglass debris came flying out

I had the ducts cleaned a week ago in the home we just rehabbed for rental. When the tech discovered the warm air ducts had fiberglass insulation inside, he just poked a hole through it and sent his thrasher in.

When I turned the system on yesterday, gobs of fiberglass debris came flying out most of the vents -except two, which have almost no flow as the main duct serving them is almost completely obstructed by ripped fiberglass. As a presumed professional and the expert in this situation, it seems he should have known better than to have thrashed the fiberglass to pieces. What are my remedial alternatives, and is it likely I hold the contractor accountable to effect a remedy?

On 2016-06-21 22:11:39.519257 by (mod) re: fiberglass is getting into the house from the air ducts

I'm a little nervous about this one.

Indeed fiberglass insulation inside of an air handler or ductwork can become damaged and start shedding - not nice to have that dust blowing into the occupied space.

But a small area of damage to the ductwork or in the air handler ought, in my opinion to be simply repairable - there is a plethora of companies offering spray on magic duct liners that might be appropriate for this situation. I'd sure not accept a $7000. job without much more compelling information. That sounds as if he's replacing the whole rooftop unit as well as all of the ductwork.

That's spending your money to reduce his risk. I've griped about this sometimes un-justified expense as have people even more famous - see

On 2016-06-21 19:28:35.220906 by Daniel Tomitz

My mom is 80. She had a guy clean her duct out and he said he found fiberglass inside the ducts and was getting in the house. It is a large rooftop ac unit might have some fiberglass linning inside if its torn do you need to replace hole unit for $7000 or can she get it repaired

On 2016-06-21 01:27:49.378471 by (mod) re: suspected fiberglass shiny "hairs" all over the place after roof repair work

Oh darn.

Look, you want to investigate some IFs

IF the roofer made a huge dusty mess that caused debris to fall into the attic - for example he tore off the roof deck entirely, down to the framing, and dropped his junk into the attic -

AND if the attic air conditioning is drawing in air from the attic space (such as torn or open or damaged ductwork)

THEN yeah you need to
- clean up the attic
- fix the HVAC system
- HEPA vaccuum the itchy dust in your house

Meanwhile change your air filters in the AC system

On 2016-06-21 01:23:19.786294 by Natalie

We recently had our entire roof replaced, been running the a/c for about a month now and just recently felt itching, its gotten so bad that my husband has welts on his skin. Upon closer inspection I noticed there are tiny little "hairs" that shine when lights hit them ALL OVER THE PLACE.

After googling I came across this page. I'm guessing it's fiber glass from all the mess made by the roofer? (He wasn't very professional) he left messes all over our garage so I can only imagine what the attic looks like. Any info will be greatly appreciated.

On 2015-10-24 18:55:51.720284 by (mod) re: yes fiberglass can come from HVAC ducts

Yes R.G. it's possible that damaged fiberglass-lined HVAC ducts could be sending fiberglass particles into the occupied space when the HVAC system is running.

Start with a visual inspection of the duct interior - by direct inspection or by using a camera system. If you can, send me photos (see page bottom CONTACT) for further comment.

On 2015-10-23 22:57:16.112091 by R Godfrey

We have had itching on our skin in a room where we had air ducts added when we completed the room. I covered the vents in the room and after completely vaccuming the area the itching seemed to stop. I think that the fiberglass inside the vents is coming apart. Does this seem possible and what can I do to fix this?

Question: how to seal fiberglass duct interiors

(Feb 25, 2014) Anonymous said:
I have solid fiberglass insulation on the inside of my ductworks. It was installed in the 80's, (this ducts are all over Florida) the air conditioner is spreading some fiberglass on the air. Can I seal that fiberglass with a special spray? There is such product on the market?


There are spray sealants for duct liners, though these are not an approach that enchants me.

  1. First, one would ask why it is necessary. If the duct interior is not damaged its original binder and coating should be intact and it should not be a source of significant indoor air fiberglass. If the ducts were damaged, say by material cleaning, it may be more effective to replace them.
  2. Second, if the concern is for mold or similar contaminants, while sealing surfaces surely reduces possible particle release, unless all of the surfaces inside the duct system are visible for inspection it might be risky to presume that a problem has been addressed by a cover-over or coating, and
  3. Third if covering harmful particles is essential one would have to be concerned about an adhesion failure, subsequent water or moisture entrapment, and future mold contamination.

While there is surely an application for spray-on sealants, with no other information I'd be nervous about the approach you suggest.

Finally, sure there are encapsulants available. InspectApedia's articles on this topic can be found beginning at


Question: flooded air conditioner in Costa Rica

(Mar 14, 2014) angela said:
I live in costa rica and have a new westinghouse 3 systems central a/c, but not new air ducts. After many problems with the system and incompetent air conditioning companies here, I have discovered that we have fiberglass air ducts.

Also, after the new system was installed, it was attached to a drain pipe that was clogged and the system completely flooded and water was all over my ceiling and the ceiling almost caved! The ducts also received a lot of water near the actual machine.

After having the system serviced 3 1/2 weeks ago, I started smelling musty, mold smell and went up the the attic (which is small and hard to navigate and veeeeery dirty) and found the entire main duct broken off of the main system (near the filter.)

It happened when the high Unqualified people were changing my filter!! All that dirt, etc was moving through my system. I am very concerned for the health of my children and my family! My children sleep where that system is pushing air!! What should I do? Do I need to change the fiberglass ducts?

They are around 14 years old or more! Also, how to get rid of mold in system? I don't even think the people here know how to service the systems properly! It is making me crazy and very nervous!!! HELP!!


Angela, Siento mucho oir de sus problemas con la systema de aire condicionando.

Most likely you will want to replace sections of fiberglass ductwork that were soaked, and to investigate where else water went in the building, as other materials may have become wet and then moldy.

Fiberglass HVAC ducts are an accepted means of air transport but if wet or dirty replacement is the effective option. Attempts at cleaning more often damage the ductwork and increase fiberglass fragment release, and spraying sealants in my opinion creates a lurking time bomb.

Question: replace rigid fiberglass air duct liner?

(Feb 25, 2015) ray said:
can fiberglass be replace in rigid air ducks our some other way to do it



Same answer as to same question you posted at

It is possible but may not be cost-effective compared with just replacing the damaged ducts.


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