What device is used to monitor temperature in a gas furnace?

The thermocouple is used in gas furnaces primarily to monitor temperature and ensure safe operation. It works by generating a voltage in response to temperature changes, providing a way to sense if the furnace is reaching unsafe levels. This function is critical because it helps prevent overheating and potential damage to the system or hazards such as fires.

In contrast, other devices mentioned have different roles. The limit switch monitors the temperature and shuts off the furnace if it gets too hot, but it does not directly measure temperature like a thermocouple does. A barometric damper regulates the draft in the flue but is not involved in temperature measurement. The inducer motor helps with venting by creating a draft but also does not monitor temperature. Thus, the thermocouple stands out as the appropriate device for temperature monitoring within a gas furnace system.