Guidelines for maintaining indoor air quality in schools with HVAC air cleaning systems are provided in this document. Information is offered on the importance of air cleaning, sources of air contaminants and indoor pollutants, types of air cleaners and particulate filters used in central HVAC systems, vapor and gas removal, and performance standards for air filters. Tips for upgrading the cost effectiveness of air filters and for maintaining and purchasing them are also provided. Three figures and three tables are included. (LMI)