The duct work in your home or office circulates the air throughout the building either heating it or cooling it as it passes through the HVAC system. Over time, the ducts can become dirty with dust, debris and mold. Those areas of build up can contaminate the air you breathe indoors.
The absence of large deposits of mold or dust in the air ducts is a good indication you may not need to have them cleaned. However, if there are allergy sufferers in the home or unexplained illnesses (especially respiratory) it may be a good idea to look into having the air ducts cleaned. Proper duct cleaning won’t cause harm to the system and may offer benefits to those living or working in the building.