On most 24 volt control systems the white stat wire is used for:

On most 24 volt control systems the white stat wire is used for:

• A. Cool
• B. Common
• C. Fan
• D. Heat

Answer: (D)

Heat calls are carried by the white wire. In a typical 24-volt thermostat system, the thermostat borrows 24V from the R supply and, when you set it to heat, it closes the circuit from R to the W terminal. That sends power to the furnace or heating device, turning on the heat. Other functions use different wires: cooling is Y, which signals the compressor; the fan is G, which runs the blower; and C serves as the common return for the circuit. So the white wire being connected to the thermostat’s heat terminal is the standard way to trigger heating.

Heat calls are carried by the white wire. In a typical 24-volt thermostat system, the thermostat borrows 24V from the R supply and, when you set it to heat, it closes the circuit from R to the W terminal. That sends power to the furnace or heating device, turning on the heat. Other functions use different wires: cooling is Y, which signals the compressor; the fan is G, which runs the blower; and C serves as the common return for the circuit. So the white wire being connected to the thermostat’s heat terminal is the standard way to trigger heating.