The E2 Models feature a tough, no frills method of supplying c lean air to a structure. Perfect for the department buying their first electric PPV or when budgets are tight. The EXP models feature a conductive, aluminum blade for the highest level of explosion protection in the industry. Perfect for the department that wants to be able to use their electric PPV for all types of ventilation situations. The VR2 series features rheostat control of speed function. Will operate on GFI circuts. The VS2 series features digital control of fan speed with a reversing fuction.