Gas Heat ESCO Practice Exam

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

1. 120 F

2. 130 F

3. 140 F

4. 150 F

The correct answer is: 140 F

The vent safety switch in an induced draft furnace should open at 140 F. This is because this specific type of furnace relies on the inducer fan to pull combustion air through the heat exchanger and out through the vent. If the vent safety switch were set to open at a lower temperature, the fan may not have enough time to properly open the switch and shut down the furnace in case of a malfunction. On the other hand, setting the switch to open at a higher temperature could potentially lead to a prolonged operation of the furnace at an unsafe temperature, increasing the risk of a fire. Therefore, 140 F is the ideal temperature for the vent safety switch to open in an induced draft furnace.