Indoor Air Quality/Fiberglass duct board


In the process of buying a house. Home inspection revealed split ac/heat pump system is 20 years old and also ductwork is all fiberglass to and from unit. My questions are...1)should I assume that fiberglass duct board is throughout the whole house and runs to each register and 2)should I consider immediately replacing it for health concerns? Thank you in advance.

Hi Sean,

More than likely, if duct board is used at all, then it would probably be duct board plenums & duct board return trunk lines, and duct board supply trunk lines, with flex supply branches to the registers. A lot of HVAC Techs like using it, because one it's cheap compared to metal, and secondly, it easier to work with when installing.

Now the thing about duct board is that the fiberglass collects & holds dust like a filter. Air flow velocity will eventually knock off those dust particles and redistribute them into your home. As well, microscopic glass particles can enter the air stream, potentially causing health issues. And the fact that fiberglass has formaldehyde that off gasses. Those are the negatives.

So I definitely would consider the option to replace it. But nevertheless, it is a material that still passes building codes, so replacing it would be solely on you. So if you are going to do this, then replace the whole duct system and start off fresh. Just make sure the contractor knows how to properly size it. You'd be surprise how many don't actually know how to do this. Airflow is a common weakness with HVAC Techs across the nation. There are few that are properly trained in that area. Anyways at a minimum, they should do a static pressure test, and make sure that you have enough return air, and the proper velocity on the supply side, with equalized distribution. Your duct system has to pull & push enough required CFM of air, in order for your Comfort System to work correctly. Airflow is like blood pressure...if your blood pressure is wrong, you are wrong. But it takes time for the damage to become noticeable...airflow affects HVAC equipment in similar matter. It's that important.

A good system should be metal plenums, with metal supply trunks, with flex supply branches, and flex return trunks. Ideally, dampers should be installed, to make air balancing easier. As well as, being insulated & sealed properly.

Sean, I hope that this heads you in the right direction. And if you have any additional questions, then please fell free to ask.

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TJ Nichols


Hello, I'd be glad to answer your questions on IAQ & other related issues!


My approach is to treat the home as one system with individual working parts. Think (TEAMWORK). When one or more areas (PLAYERS) are failing or bad, it affects the whole system (TEAM) to operate less efficiently. I aim to address the problem, not just the symptoms, to offer better solution options.

High School Grad (06/1991)(VA) EPA licensed & certified in Types I & II Refrigeration (04/1997)(MD)

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