On a call for heat, the thermostat energizes which terminal?

When a heating system is called for heat, the thermostat typically energizes the W terminal. The W terminal is specifically designated for the heating signal. When the thermostat detects that the ambient temperature has fallen below the set point, it completes the circuit by sending a voltage signal to the W terminal, which activates the heating system.

In a conventional system, this signal triggers the furnace or heating mechanism to start producing heat, thereby warming the space to the desired temperature. Understanding the role of different terminals can help in diagnosing issues in heating systems as well as ensuring that the thermostat is connected correctly for optimal operation.