Indoor air quality is an area of increasing concern in the United States. While most people are aware of the threat posed by outdoor air pollution (such as smog), few realize that inside homes, schools and offices one can be exposed to two to five times as many pollutants as outdoors, according to the U.S. Environmental Protection Agency. Indoor air pollution has been ranked as one of the top five environmental risks to public health by the EPA and its Science Advisory Board. In addition, the U.S. Occupational Safety and Health Administration has estimated that 30 percent of Americans who work in non-industrial buildings are exposed to indoor air pollution.

During the 1970s energy crisis, buildings were designed to be airtight, conserving as much warm air during the winter and cooled air during the summer as was possible. Windows that could not be...