Research
According to the World Health Organization, approximately 30 % of all commercial buildings have significant indoor air quality problems. This shows itself by occupants suffering cold or flu-like symptoms, serious health effects such as Legionnaire's Disease are also possible.
The American College of Allergist states that 50% of all illnesses are either caused or aggravated by polluted indoor air.
Sick Building Syndrome
The United States EPA released a publication on "sick building syndrome" in 1991. The first cause for sick building syndrome listed was inadequate ventilation, which may occur in the HVAC system, not effectively distributing air to the people in the building. The United States EPA recommends the routine maintenance of the HVAC system.
General symptoms of airborne irritants or pollutants include:
fatigue, headaches, allergies, sneezing, sore throat, coughing, runny nose, watery eyes, forgetfulness, etc.
These particles are routinely found in heating/air conditioning duct.
Recommendation
Air Clean Duct Cleaning Company Recommends the following:
Clean your carpets yearly, your upholstery and drapes every 2 years.
Replace your filters every 1-3 months
Clean and sanitize your ducts every 3-5 years.