Fiberglass seems to be a part of ductwork these days. You cannot get a standard ventilation system installed without it. If you do not want tiny pieces of glass included in your air system you must specifically request it not be present. This practice has become widely accepted. Has anyone ever mentioned to you the shelf life of the fiberglass that is added to the air ducts? It does have one. Yet no one seems to think of it or mention it. When the fiberglass inside the vents and or plenum begin to deteriorate the blown glass becomes part of the air we breathe. I personally can feel the tiny particles even in a new HVAC systems via soreness in my sinuses, tightening of my lungs and a burning, dry feeling in my eyes, but not every one is that sensitive and most do not notice it in the air, or do not make the connection to what they are feeling.
Every time the heater would kick on the air would make the people in the house feel sick. When they took the floor vent covers off to clean them, this is what they found. Fiberglass.
If you look closely you can see the foil and fiberglass down the vent in the floor. (The first picture on this page shows a close-up.)
Fiberglass somewhere inside the ductwork was breaking apart and blowing into the air.
You can add a non-fiberglass filter to try and block the glass from becoming airborn, but always remember that the tiniest of particles, the ones you cannot see that are the most dangerous to the lungs, will not be stopped by a filter. The best way to handle the problem is to removed the fiberglass.
If someone in your family has been getting sick or just feels sluggish with low energy, don't forget to consider the air quality in the home. People think of the food they eat and how much exercise they get, but rarely think of what they are breathing in. Always remember that Air Matters.