With some exceptions, blowers should not be operating when the furnace is off. People may set the blower to run continuously if they choose. Multi-speed direct drive blowers can also run at low speed to filter and humidify air when the furnace is not on. When the furnace kicks on, they will operate at a higher speed.
Fans running continuously may be a homeowner choice, a broken fan switch or an improper wiring arrangement.
Cool, unpleasant drafts may be experienced. Electrical costs will be higher and the fan and motor life may be shortened.
If the fan is running continuously, check to see if the
switch has been set to control this. Sometimes these switches are broken or stuck in the On position. In the
position, the fan should run only when the furnace is on.
When you operate the furnace, notice whether the fan speed changes. It's possible that the fan is running on low speed by design.
If you do not intend to have the fan running continuously, it's possible that the fan control switch is defective or has been by-passed. Where the fan is running continuously for no apparent reason, we recommend servicing to verify that the fan and limit functions have not been compromised.