Make sure that the company has the proper equipment and enough HEPA filtered vacuum power (2,000 CFMs or more), to properly clean your air ducts. Be weary of companies that use small vacuum units that have a small rotating brush on the end of a small vacuum hose with a typical airflow of 150 to 300 cfm or less. Proper air duct cleaning vacuums are negative air machines with 2,000 CFMs have 8 inch to 14 inch or larger, vacuum hoses to capture large quantities of dust and debris.
"This a very professional company that came the next day after being contacted late in the day prior. The two guys that came to the door that did the work were well dressed and very courteous. They cleaned my diver vent and it works perfectly. I have their literature and will be calling them when I m ready for duct cleaning. Nice equipment too! Thanks for the good work. Nice not to have scroungy guys showing up at the door. "