You can hire a home air duct cleaning contractor to clean and maintain your air ducts as often as you want, as long as the service is completed properly, it will not harm your home, ducts or HVAC system.
Cleaning air ducts can improve your HVAC efficiency; however, it may not be as effective as a service check on your HVAC unit itself.
In fact, you really only need air duct cleaning when the following things are evident...
You or someone in your family is suffering symptoms that have been related to poor air quality by a doctor and you suspect that your home air ducts have allergens, mold or excessive dust inside of them.
In this case, you should get your air ducts inspected by a licensed air duct cleaning specialist, and ask to see evidence of the pollutants, dust, or mold to be removed before hiring them to clean your ducts.
Your heating or cooling system is functioning poorly, and it is suspected that poor ventilation is the problem.
There are rodents, pests or other animals living inside your ducts.
There is a large amount of mold growing inside the ducts, or on the components of your furnace or A/C (heating and cooling systems).
Your air ducts haven't been serviced or cleaned in several years, and there are visible amounts of dust collected on them.
Keep in mind that although cleaning your heating and cooling ducts is not necessary, it is not harmful either-unless it is done incorrectly.
Cleaning ducts with the wrong materials or cleaning them in a way that is harmful can actually cause more damage, by releasing dirt, allergens and dust into the air, and cracking the ducts or damaging your heating and cooling system.
Home air duct cleaning can improve air quality if there are allergens, dust or mold inside your air ducts, and in some cases it may even improve the operation of your furnace or A/C, if your HVAC system requires a lot of ventilation.
If you would like to keep your air ducts clean, find a reputable air duct cleaning contractor and have your air ducts cleaned regularly.