What occurs when the switch closes between the R and W terminals of a thermostat?

When the switch closes between the R and W terminals of a thermostat, it completes the circuit that signals the heating system to activate. The R terminal generally represents the 24-volt power supply from the transformer, while the W terminal is connected to the heating system's relay or control circuit. Closing the switch essentially sends 24 volts to the heating system, prompting it to turn on and start producing heat.

In heating systems, the operation of the thermostat is critical for regulating temperature. By connecting R and W, the thermostat indicates that heating is required, thus engaging the furnace or boiler to begin the heating process until the set temperature is reached. This function is vital for maintaining comfort within a space during colder months.

The other options do not accurately reflect the operation of the thermostat in this scenario. For instance, closing this circuit does not activate the cooling system, initiate fan operation, or turn off the thermostat. Instead, it directly invokes the heating mechanism, making it essential for effective climate control in homes and buildings.