The primary difference is in the type of controls the units use. The Model VH2 (Vortex Heater) has a bi-metal thermostat and a “plus-to-minus” temperature control dial. The unit offers a selection of 1500 watts on “High” or 750 watts on “Low”. The thermostat will cycle the unit on and off as it reaches the point of heat selected on the dial on top of the unit. Safety features on the VH2 model include an instant Tip-Over switch that cuts the power if the unit is tilted or knocked over and a cool-touch cabinet and grill. It also features Over-Temp protection, which automatically shuts off the heat if the airflow is blocked, plus a backup fuse for an added layer of protection. The Model DVTH (Digital Vortex Heater) features a thermistor, a sophisticated sensor that allows the unit to self-adjust the heat output to maintain the desired temperature. You select the temperature using the calibrated temperature control dial on the top of the unit. The DVTH maintains a constant room temperature