I have lived in the same house now, for over twenty years.
I have been through many things in this house.
We have had two hurricanes bombard us, several springs where the creek rose, and a couple of horrendous summer storms that have ripped off the roof and drenched the inside of our home. We even had some honey bees take up residence in our chimney, one time. With all of the things that have happened to our home, I couldn’t believe that no one had ever cleaned the ductwork. After flooding, wouldn’t you have thought the HVAC company would have thought to clean the ductwork when they were cleaning the HVAC system. I would have thought the ductwork was a part of the HVAC system, but it doesn’t seem that way to the HVAC company. I had called them to do the regular maintenance on my furnace. While the HVAC technician was working on the furnace, she noticed a lot of dust and debris that was on the floor near the air duct vent. She asked us when the last time was that we had the ductwork cleaned. I just shrugged because I couldn’t remember ever calling to have someone clean the ductwork. She told us the ductwork should be cleaned every other year, at a minimum. They sent a professional ductwork cleaning crew to our house the following day. I don’t plan on waiting for two years. Next year and every year after, they can clean the ductwork when they do the annual maintenance and service on our furnace