When running the furnace fan all the time, the air is constantly circulating, helping to eliminate hot and cold spots in rooms. The air is also being filtered, helping remove pollen and dust from the home.
Increased Utility Bills
According to the state of Wisconsin's Focus on Energy program, running the furnace fan all the time adds substantial cost to heating a home, even with energy efficient furnaces.
The state of Wisconsin does not recommend running the furnace fan constantly. The extra kilowatts used end up adding to the cost of heating the home and it shortens the life span of the fan.