The air duct is totally neglected

I’ve lived in our home for almost twenty years and have regularly been truly conscientious about scheduling annual repair for our furnace and A/C, however every September, I call up the local Heating, Ventilation as well as A/C business and set up an appointment for a thorough inspection, tuning and cleaning. I call back in May to have the A/C ran tests on.  The professional resolves any troubles with wear and tear, and removes any buildup of contaminants. Because of this proper upkeep, I expect the heating and cooling system to operate at peak capacity and efficiency. I suppose it will maintain a comfortable temperature and give a healthy home. I was both surprised and frustrated when the furnace failed to live up to demand last Wintertime.  I observed the heating system was running for longer cycles and struggling to maintain an even, comfortable temperature. There were freezing pockets in many rooms, and the heated air had an unpleasant, musty smell. Whenever the furnace started up, our whole family would start coughing, sneezing and complain of headaches. There was really an excessive amount of dust flying around. When I saw how high our biweekly energy bill was, I finally called for heating repair. The Heating, Ventilation as well as A/C professional found no problems with the furnace. When he checked the duct system, however, he discovered an spine-chilling accumulation of contaminants. There was dust, dirt, bugs, webs, decomposing rodents, and mold growth hidden within the ducts. The troubles with the duct system were responsible for our degraded air quality, diminished comfort and greater energy consumption. I was a bit annoyed that the Heating, Ventilation as well as A/C professional had never suggested repair for the duct system. Since it’s nearly truly concealed in the walls, ceilings and crawl spaces, I never thought of it.