What is the maximum temperature on a fan high-limit switch?

What is the maximum temperature on a fan high-limit switch?

• A. 240°F
• B. 230°F
• C. 250°F
• D. 260°F

Answer: (C)

A fan high-limit switch serves as a safety guard that opens the circuit when the furnace air stream reaches a set maximum temperature to prevent overheating. The trip temperature is chosen so that cooling is enough to protect the equipment but not so low as to cause nuisance shutoffs. About 250°F is a common rating for this purpose: it allows normal operation and heat soak during peak demand, then cuts power to the burner if temperatures rise too high. If it were set lower, it would trip too often during normal operation; if higher, the system could overheat before protection engages. After cooling below the reset point, the switch will allow the furnace to restart.

A fan high-limit switch serves as a safety guard that opens the circuit when the furnace air stream reaches a set maximum temperature to prevent overheating. The trip temperature is chosen so that cooling is enough to protect the equipment but not so low as to cause nuisance shutoffs. About 250°F is a common rating for this purpose: it allows normal operation and heat soak during peak demand, then cuts power to the burner if temperatures rise too high. If it were set lower, it would trip too often during normal operation; if higher, the system could overheat before protection engages. After cooling below the reset point, the switch will allow the furnace to restart.