Insulated EXP rated air handler One of two units, each delivering 9,000 CFM and designed for use in a Class 1, Division 1, Group D hazardous environment, 4&#039;&#039; double walled construction with fiberglass packing, 250,000 BTUH heating with a 50% water/glycol mix and coil package, inlet and discharge mufflers were required to achieve 70 dBA at 3&#039;