Air duct cleaning service providers may tell you that they need to apply a chemical biocide to the inside of your ducts to kill bacteria (germs) and fungi (mold), and prevent future biological growth. Some duct cleaning service providers may propose to introduce ozone to kill biological contaminants. Ozone is a highly reactive gas that is regulated in the outside air as a lung irritant. However, there remains considerable controversy over the necessity and wisdom of introducing chemical biocides or ozone into the duct work.
If you are replacing your air conditioning system, make sure that the unit is the proper size for your needs and that all ducts are sealed at the joints. A unit that is too big will cycle on and off frequently, resulting in poor moisture removal, particularly in areas with high humidity. Also make sure that your new system is designed to manage condensation effectively.

I own a small mechanical company. My main work is service and system replacements. I have never been a believer in duct cleaning. The company I worked for before had our duct man come out and do my house. I saw no difference. Preventive maintance is what I recomend. Remove fan and clean, seal fan compartment to prevent dust from being pulled in, filters I install media filters, they are 5″ thick and pleated. I have tested them to make sure static presure was not a issue. Heat exchangers and AC coils need to be cleaned. I will tell you this to do a good cleaning I usually spent 1-2 hrs, When I’m finished I would not have a problem eating my diner on the system. Good filters, clean system and properly tuned up are my recomdation to anyone. I’ve included my email feel free to contact me with any questions.

Some research suggests that cleaning heating and cooling system components (e.g., cooling coils, fans and heat exchangers) may improve the efficiency of your system, resulting in a longer operating life, as well as some energy and maintenance cost savings. However, little evidence exists that cleaning only the ducts will improve the efficiency of the system.