Next to your roof on your house, the air In your home could possible be the most valued asset your home has to offer. It keeps you warm in the winter and cool in the summer. Your HVAC unit will circulate your home's air four times per hour while your filter is removing most floating debris such as dust, pollen, dander and any other smaller microscopic things like bacteria and mold spores. Not all mold spores are filtered, which causes spreading these nuisances throughout our home, while most of these are non harmful they can be dangerous for others. Most heating and cooling company's that service your home's unit don't even clean air ducts ??? And they consult their customers with bad advice of when to change their filters. I've heard home owners state they were told every 3 to 6 months . With this one bad piece of advice it has created a industry selling new units and the quality of the air has never changed. Being in the indoor air quality industry for 20 years I have found if a home owner changes their filters every 30-60 days the unit will last way past its life expectancy and provide the cleanest air for the home.
There are several types of cleaning methods in the industry today, how they do it really depends on your geography. Home's on land with good drainage have basements, home's with poor drainage have a crawl space or slab. The first cleaning method is the push pull method that uses a negative air machine to reverse the flow of your home's air and filters air through a Hepa filter. The technician will enter each register with a duct agitator that uses very high compressed air to clean the internal lining of you ducts and pushes debris to the negative air machine. The other method is direct contact cleaning with a rotary brush and a strong vacuum attached that is also Hepa filtered. Any professional air duct cleaning company would have both of these system. If they do not, they are new to the business or have not learned about every type of home.