We bought an older home and renovated it. We added an extension, and that required adding on some air ducts and getting a more powerful furnace and air conditioning system to provide enough heat and cool air now that the house was bigger. The old furnace actually did not output enough BTUs to heat the place appropriately before the addition. We gutted the place and put in all new insulation, so that helped a lot. We failed to do one thing we never considered, and that is why we got a company that does air duct cleaning in Walnut Creek to come out and clean out all the old air ducts.
We noticed dust, grit and grime on furniture when we turned the new furnace on. It was not in the new addition; it was just in rooms that had the old ducts. I pulled off the vent cover in the living room and noticed a lot of buildup. The source of the dirt was in the ducts. It was breaking loose and getting into the rooms. The air handler now pushed a higher volume of air, and that was helping to break loose the built up grime in the air ducts. The company that does air duct cleaning in Walnut Creek came out and thoroughly cleaned every one of the old ducts. The new ducts were only a couple of months old, so they did not need cleaned.
We have a HEPA filtration system and one of those electrostatic filters that grab particulates before they get to the blower. We probably will not need our ducts cleaned again as long as we maintain the filtration system. However, the old ducts were dirty because of years of use with standard furnace filters that do not trap a lot of particulates. Over the years the airborne particulates built up on the interior surfaces of the air ducts. Now they are squeaky clean!