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Indoor Air Quality/deteriorating fiberglass duct board inside air handler


fiberglass duct board
fiberglass duct board  

I recently had the gas furnace and air ducts in my townhouse cleaned (20 yr old HVAC system, in Seattle WA). I did so because a few months after purchasing the house, I noticed what appeared to be paint, paint texture spray and dry-wall dust inside some of the ducting. It appears that at some point the HVAC system was left running during construction and painting and all the debris was sucked in. Besides the visual evidence of the debris, I didn't notice any odd smells or an extraordinary amount of dust coming from the system. However, one of my cats developed feline asthma (it's a real thing!) and I noticed a slight increase in my general stuffiness and congestion, especially in the mornings.

I did my research and choose a company certified by NADCA ( The entire system was cleaned using air-whip technology and a strong truck mounted vacuum. Basically the air dislodged the dust and debris inside the ducting and the vacuum sucked it up. After the cleaning, the technician had me inspect his work inside of the air handler on the furnace. He did a pretty good job with the cleaning, but there was no way he could remove the stuck on paint and texture spray.  

My big concern (and the reason for this question) was raised when I noticed that the material lining the cabinet was deteriorating (I did some research and identified it as fiberglass duct board). I don't have any idea how long it's been like that because I had never looked in the air handler before the cleaning. And, when I purchased the house I did not have an inspection done because the property was bank-owned and sold as-is. I know now that for my own health and safety I SHOULD have had an inspection, but I was a first time home-buyer and figured if the bank wasn't going to pay for any needed repairs, there was no point.

I am now concerned that fiberglass particles may enter the air stream and negatively effect our health. Indoor air quality testing is expensive (got a quote for $500) and so is replacing the hvac system. But, our health is important so I want to make sure to do the right thing -- I just don't know what the right thing is. Replace the entire system? Replace the part of the system lined with ductboard? Turn off the system and install a ductless system? Have the air tested and if the levels of fiberglass are low to absent, do nothing?

I would appreciate your expert advice!


Typical wrapped metal duct
Typical wrapped metal  

A couple of things:

Fiberglass duct needs to be cleaned VERY gently, otherwise fiberglass particles can be dislodged.  In my opinion, fiberglass ducts and fiberglass-lined metal ducts are not good candidates for cleaning.  They are just too fragile.

In your case, I would replace the fiberglass duct or duct liner and use a sheet metal duct with external insulation.  This way, the duct is smooth metal inside, easy to clean, and much less likely to harbor microbes and dust than a porous liner.  See attached picture.

Best of luck, and please let me know if you have any additional questions.

Steve Major

Indoor Air Quality

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Stephen Major (Principal--Lakeland Environmental)


I can answer questions on indoor mold, indoor air quality, asbestos, and indoor moisture problems. This includes mold testing and mold remediation. PLEASE indicate your state or region, so I can provide the best possible answer.


I have extensive experience in the investigation, testing, and remediation of indoor fungal (mold) infestations, including the design and oversight of remediation projects, hands-on cleaning and removal, and safe work practices. I developed a successful mold remediator training and certification program, and have trained many mold workers and remediation supervisors in proper techniques. I have a strong knowledge of the ways in which moisture and airlow patterns in buildings can affect fungal growth and air quality.

BS Cornell University. IAQA Certified Mold Remediator. 40-hour HAZWOPER certification. NYS Department of Health Certified Training Director.

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