At what temperature should the vent safety switch in induced draft furnaces open?

The vent safety switch in induced draft furnaces is designed to prevent dangerous conditions by monitoring the temperature of the exhaust gases. When these gases reach a specific temperature, the switch is triggered to open, thereby shutting down the furnace operation. This safety feature is critical to ensuring that the system does not overheat and potentially cause a fire or other hazardous conditions.

The correct answer of 120°F is a standard setting used in many systems to provide a safeguard against excessive heat. At this temperature, it is adequate to ensure that if there is a fault in the venting system—such as blockages or inadequate airflow—the switch will open, preventing the furnace from operating in an unsafe condition. Properly functioning vent safety switches are essential for maintaining the safety of furnace installations, as they effectively respond to rising temperatures that may indicate safety issues.

Higher settings might not respond as promptly to dangerous conditions, while lower settings could lead to unnecessary shutdowns or nuisance trips, making 120°F a balanced and effective choice for ensuring safe operation in these scenarios.