In typical HVAC control circuits, what does the W wire represent?

In typical HVAC control circuits, what does the W wire represent?

• A. W = power
• B. W = common
• C. W = heat
• D. W = cooling

Answer: (C)

W is the heat call wire. In a typical 24‑volt thermostat circuit, the thermostat sends 24 volts from the R supply to W when heat is needed. Closing the R–W path energizes the furnace control, turning on the heating stage (gas valve or electric heat) and, after a short delay, the blower. That means W is a control signal for heating, not the power supply or a common return. The other designations are R for the hot power supply, C for the common return, and Y for cooling. W is commonly white and may also be used for auxiliary heat in heat‑pump systems.

W is the heat call wire. In a typical 24‑volt thermostat circuit, the thermostat sends 24 volts from the R supply to W when heat is needed. Closing the R–W path energizes the furnace control, turning on the heating stage (gas valve or electric heat) and, after a short delay, the blower. That means W is a control signal for heating, not the power supply or a common return. The other designations are R for the hot power supply, C for the common return, and Y for cooling. W is commonly white and may also be used for auxiliary heat in heat‑pump systems.