I have consistently been undoubtedly conscientious about replacing the air filters in the gas furnace and air conditioning every week; I schedule professional service for the heating system in the fall and the cooling system in the Spring. I am not sure why I forgot about taking care of the ductwork. I guess that because the pipes are hidden in the walls and ceiling, I just never considered the need for service. I was not cheerful when our gas furnace had trouble keeping the house moderate last winter, and the furnace seemed to be running non stop and yet the temperature was inconsistent from one room to another; No matter how high I adjusted the control unit, the house felt chilly. The gas furnace is not that ancient and should have been able to handle the cold weather. I also observed that there seemed to be a lot of dust floating around, and our weekly utility bills were higher than normal. I finally hired an Heating and Air Conditioning corporation to check out our gas furnace. The corporation maintained the furnace and found that the problem was caused by the ductwork. There was a considerable buildup of contaminants in the pipes. The accumulation of dust, pet dander, pollen, mold growth and even dead rodents was blocking airflow through the pipes, because the maximum amount of air was failing to reach the several rooms, it was forcing the gas furnace to run more often, work harder and use more energy. There was greater wear and tear on the furnace. The corporation gave a duct cleaning service using equipment that looked a lot like an industrial vacuum cleaner.