A laboratory ventilation system isolates and protects occupants from hazardous fumes and provides the minimum outside air at a comfortable temperature. A significantly greater volume of conditioned makeup air is needed for fume removal than is required for conditioning the space. A once-through system usually is used due to the high exhaust quantity and the desire to isolate laboratories from adjacent spaces. The high costs of high airflow systems are magnified by the constant operation found in laboratories. Unfortunately, the common design approach often does not recognize these unique aspects of laboratories.