Indoor air quality can have a significant effect on your health. Studies show that people spend 65 to 90 percent of their time indoors, and indoor air can be two to five times more polluted than outdoor air. The young, elderly, chronically ill, and those with respiratory or cardiovascular disease are often the most impacted by poor indoor air quality.
Fresh Air for a Healthier Home, Guide to Ventilation Systems
Content Source: Indoor Air Quality Program