PROVIDING a comfortable and healthy indoor environment for building occupants is the primary concern of HVAC engineers. Comfort and indoor air quality (IAQ) depend on many factors@ including thermal regulation@ control of internal and external sources of pollutants@ supply of acceptable air@ removal of unacceptable air@ occupants' activities and preferences@ and proper operation and maintenance of building systems. Ventilation and infiltration are only part of the acceptable indoor air quality and thermal comfort problem. HVAC designers@ occupants@ and building owners must be aware of and address other factors as well. Choosing appropriate ventilation and infiltration rates to solve thermal comfort problems and to reduce energy consumption can affect indoor air quality and may be against code@ so such procedures should be approached with care and be under the direction of a registered professional engineer with expertise in HVAC analysis and design.