See here how Rotobrush duct cleaning works:
We use one of the most sophisticated and effective air duct cleaning systems on the market today ROTOBRUSH Duct Cleaning System. Our advanced method thoroughly scrub and vacuum ducts without harsh chemicals.What is left behind is fresh, clean, virtually irritant-free air inside your house.
Our complete air duct cleaning process includes:
-removing and cleaning all supply vents
-brushing and vacuuming all dust mites,
pollen, dead skin cells, and household dust inside the air ducts.
-we will sanitize (if desired) your air ducts and vents with
an environmentally safe sanitizer commonly used in hospitals and nursing homes.