This chapter explores “low cost-no cost” areas that should be investigated in the heating, ventilation and air-conditioning Energy Audit. The most effective means to deal with an Indoor Air Quality problem is to remove or minimize the pollutant source, when feasible. If not, dilution and filtration may be effective. Improved filtration can include enhancements such as ionization devices to neutralize airborne biological matter and to electrically charge fine particles, causing them to agglomerate and be more easily filtered. In addition to reducing air flow during occupied periods, consideration should be given to shutting the system down during unoccupied hours. Desired relative humidity requirements are achieved by vaporizing water into the dry ventilating air. Most humidification systems are used to maintain the comfort and health of occupants, to prevent cracking of wood, and to preserve materials. Computer program analysis is a very important design tool in the energy audit process.