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Feeling Ducty!

air ducts
Reading Time: 3 minutes

Hey everyone, welcome back and Happy Friday as always. Who is that masked man in the accompanying image you ask? That’s me with my PPE (Personal Protection Equipment) after pulling out some old, mold infested duct board from one of our customer’s attics. Yummy right? Last week we talked about the importance of a sealed duct system, today I would like to focus on ductwork that is going to be older than 15 years, and primarily we will be discussing duct or fiber board.

First off, there are many different types of ductwork than can be found in a typical home setting, ranging from flexible style, which is a rigid plastic supported by a spiral wire and wrapped in fiberglass insulation, to metal piping, which is rigid and also insulated with either a thermal foam or again wrapped in fiberglass insulation.


Then we have duct board (or fiber board), which is made of compressed fiberglass particles to form a sheet similar to a sheet of drywall. It is typically manufactured in either one or one and a half inch thickness, and has an aluminum foil style coating on the outside to further reflect heat and give it better insulating properties.

I know you are looking for segue between duct board and mold, right? The simple answer is that mold needs three things to be really, really happy and those are; a food source, darkness and moisture. It sounds like the inside of a duct system is the perfect place for biological growth especially in older fiberboard duct systems. I asked one day why would the industry use something that is perfect for mold growth to design an air distribution system. A very wise man, (I believe it was Arthur D’Attile), replied very simply, “try as we might there is no way to really engineer for the future”. One must remember we have only been doing serious air conditioning for 50-60 years now and we certainly didn’t know then what we know now.

When duct board was first invented, they did not take into consideration the long term effects of what could be going on inside that duct system, and as a matter of fact, we didn’t quite really grasp the ramifications until the late 1990’s. As with any industry we adapted, and now we use an antimicrobial duct board in today’s systems that don’t allow for biological growth. We also use antimicrobial paints on the interior of ducts to do the same.

Now for the bad news… There isn’t a lot we can do for duct board that is more than 15 years old and has biological growth inside it other than to replace it. The Indoor Air Quality Association does recognize coating the interior of the duct system with an antimicrobial paint as an acceptable repair to improve indoor air quality, although they do note it is not considered best practice. Unfortunately, the best practice is to simply replace all duct board components of the air distribution system if your home has this issue.

Also for all my condo owners out there, you have a 99.9% chance that the air distribution system in your condo is duct board. I know I’m just full of great news today! That said, if you are experiencing respiratory issues, allergies, or some other unexplained illness, it might be time to look at the air distribution system in your home to see if that is perhaps the cause of your malady. There are over 5,000 types of mold in the world and every person has a different reaction to every different type, so you can never rule out your ductwork unless you have it checked out. The Comfort Consultants at Art Plumbing, Air Conditioning & Electric are the perfect folks to do it for you! Give us a call at 1-888-475-1504 or visit to schedule your Duct System Evaluation today.

House Whisperer out!


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