Which control is used to initiate the operation of the induced draft blower in a high-efficiency furnace?

The thermostat is the control that initiates the operation of the induced draft blower in a high-efficiency furnace. The thermostat senses the home's temperature and sends a signal to the furnace when heating is needed. Once the thermostat detects that heating is required, it activates the system, including the induced draft blower, which is responsible for ensuring proper ventilation and exhaust of combustion gases.

This process is critical because the induced draft blower creates a negative pressure that helps draw air into the burner assembly and expel flue gases out of the furnace, promoting efficient combustion. The operation of the blower generally occurs before the ignition sequence to ensure that the combustion chamber is cleared of any residual gases, providing safety and optimal performance for the furnace.

While other controls mentioned have important roles in the operation of the furnace, they do not initiate the blower's operation in the same way that the thermostat does. Pressure switches monitor system pressure, ignition controls manage the lighting process, and interlocks ensure safety by preventing certain operations unless specified conditions are met. However, it is the thermostat that starts the overall heating process, making it pivotal for initiating the draft blower's operation.