Current studies have revealed that air quality in 19 out of 20 homes was "considerably more polluted than air outside."
According to the National Air Duct Cleaners Association (NADCA), the proper method for duct cleaning is to place the system under negative pressure along with a strong vacuum. Various brushes and cleaners are placed into the ducts to remove debris, which will flow to the vacuum. NADCA guidelines allow vacuum equipment that eliminates particles outside of the house, and inside-exhaust systems that utilize the HEPA filters.