What you should consider when hiring a duct cleaner
Some duct-cleaning companies clean heating and cooling equipment (condenser coils, fan blades, etc.) as part of a comprehensive duct cleaning, and some charge less if you skip this step. Your heating and the air-conditioning contractor may do this for you, but don’t assume these services are part of regular maintenance; be sure to ask explicitly.
Steps You Can Take.

Complete System Cleaning
To the following pieces of information should be consider with every air duct cleaning.
4 x Year
Replace Filter
Air quality starts with the furnace air filter. Replace quarterly if you can.
70%
Blower Dirty
During an air duct cleaning the blower fan is usually dirty 70% of the time.
50%
AC Coil Dirty
Common during an air duct cleaning. The coil is dirty 50% of the time.