It is considered OK to continuously run a furnace fan. Homeowners should experiment to see if it works best for their home to have the furnace fan running continuously or not. If homeowners find this is beneficial, it is generally suggested to only run the furnace fan constantly during the cold heating season. There are several benefits and some drawbacks to running a furnace fan constantly.
When the furnace fan is constantly on, air is continuously cycling throughout the home. This is beneficial because it can reduce cold and warm spots in the house. In addition, it provides extra air filtration which may be helpful if health risks are a concern. Some HVAC technicians also state that it is better for the fan motor to run continuously instead of turning on and off with the furnace.
Running a furnace fan constantly also has drawbacks. First of all, depending on the type of motor the furnace has, having the fan on continuously may add several hundred dollars to the home's electric bill. Newer motors called ECM motors are more energy efficient than older AC motors. Second, having a fan run constantly leads to higher dust levels in a home, even with expensive furnace filters.