The number of stages refers to how the snowthrower moves the snow. A single stage snowthrower uses the front auger to sweep and throw the snow in a single action. Single stage machines are designed for lighter-duty applications, such as small driveways, steps and short sidewalks. They are generally lightweight, maneuverable and easy to use -- ideal for areas where snowfall is relatively light to medium throughout the winter.
Dual stage snowthrowers use the front auger to sweep the snow and feed it to the impeller. The impeller then propels the snow up and out the chute. The auger turns slowly to control the amount of snow the impeller throws. Dual stage snowthrowers are designed for heavier applications, such as larger driveways or long sidewalks -- great for areas where conditions range form moderate to extremely heavy, wet snow.