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The vent safety switch on induced draft furnaces is designed to ensure safe operation by preventing furnace operation when venting issues arise. Typically, this switch will open at a temperature of around 140°F. This designation helps to protect both the furnace and the occupants of the building from dangerous conditions such as overheating or improper venting of combustion gases.

When the temperature in the venting system reaches this threshold, it indicates that there may be inadequate airflow or blockages that could lead to the accumulation of harmful gases. Therefore, the safety switch interrupts the furnace operation, allowing the system to cool down and ensuring that flue gases are properly evacuated. This critical safety feature plays a vital role in maintaining the safe performance of the heating system.

The options of 80°F, 100°F, and 120°F are typically too low for the vent safety switch to activate, as manufacturers often set these thresholds higher to require more significant temperature changes that indicate actual performance issues. Thus, the temperature of 140°F is consistent with standard practices in the industry, supporting both safety and operational integrity in induced draft furnaces.