In a heating system, with the fan switch set to AUTO, which motors run when the thermostat calls for heat?

In a heating system, with the fan switch set to AUTO, which motors run when the thermostat calls for heat?

• A. Blower and exhaust motors
• B. No motors
• C. Only the blower motor
• D. All three motors

Answer: (D)

When heat is called for, the system powers through a sequence that involves all the motors in the furnace’s air- and exhaust-path. The exhaust/inducer motor starts first to purge combustion gases and create a draft, then ignition occurs, and after a brief delay the blower motor comes on to push the heated air through the ducts. In many furnaces there’s a third motor in the ventilation or damper path that also runs to support proper venting and airflow during the heating cycle. With the fan switch set to AUTO, the blower is engaged only during active heat (and cooling) cycles, but during the heat call the blower, the exhaust/inducer motor, and the third motor all operate as part of the heating sequence. That coordination ensures safe ignition, proper venting, and efficient distribution of warm air.

When heat is called for, the system powers through a sequence that involves all the motors in the furnace’s air- and exhaust-path. The exhaust/inducer motor starts first to purge combustion gases and create a draft, then ignition occurs, and after a brief delay the blower motor comes on to push the heated air through the ducts. In many furnaces there’s a third motor in the ventilation or damper path that also runs to support proper venting and airflow during the heating cycle. With the fan switch set to AUTO, the blower is engaged only during active heat (and cooling) cycles, but during the heat call the blower, the exhaust/inducer motor, and the third motor all operate as part of the heating sequence. That coordination ensures safe ignition, proper venting, and efficient distribution of warm air.