Third and last on our series of furnace feature discussion, we are going to cover the variable speed motor/fan.
As the name implies, the variable speed motor is capable of adjusting the air flow to fit various duct configurations, heating/cooling applications, and ramps up in ways to provide the quietest operation possible for your duct system. This is in contrast to the older furnaces that has constant speed or multi-speed motors. If special type of filters like electronic air cleaner or high efficiency media filter are desired the variable speed fan is capable of running in a very low speed to recirculate air.
Certain manufacturers also take advantage of the variable speed fan in zoning systems to make air flow seemless for its operation. This is a big plus for zoning retrofit applications.