In the thermostat wiring, which terminal is used for the heating control?

• A. C
• B. R
• C. W
• D. Y

Answer: (C)

The heating control is sent through the heat call input on the thermostat. When you set the thermostat to heat, it closes the circuit from the 24V supply to this heat input, which tells the furnace to start heating. The common terminal isn’t used to start heat; it’s just the return path for power in some thermostats. The cooling terminal controls the air conditioner, not the furnace, and the power terminal provides the 24V supply to the thermostat itself. In practice, the wire for heating is typically the white wire connected to the heat call input, which is often labeled for heat on many thermostats.