The air conditioning coils, air exchanger compartment and the furnace itself, are a must, when cleaning your air ducts, and only takes the cleaner an extra minute or two to clean. My advice here would be to go with a company that includes the air conditioning coils, air exchanger compartment and the air cleaning furnace for one flat fee (usually this only applies to homes with one furnace, additional furnaces usually means you have a rather large house, or the crew has to set up the equipment twice).