While no one can say with complete certainty that clean air ducts promote better indoor air quality, there’s little doubt that dirty ones collect contaminants like dust, pet dander, and chemicals. A six-room home can collect as much as 40 pounds of this each year, according to the HVAC Inspection, Maintenance, and Restoration Association (also known as NADCA).
Professionals who have been specially trained to use Rotobrush equipment can remove these contaminants altogether.   The US Environmental Protection Agency says homeowners should consider cleaning air ducts when:

• There is visual evidence of mold growing inside ducts or on other HVAC components.
• Mold can only be positively identified by an expert; final confirmation may require a laboratory test.
• Ducts are infested with vermin such as rodents or insects.
• Ducts are excessively clogged with dust, debris, or particles and are getting released into the home through the supply registers.

NADCA notes that contaminant buildup can also block airflow and force HVAC systems to work harder and for longer periods of time. This can increase energy bills and wear and tear on the systems themselves.

Credit: www.rotobrush.com