Which control is typically found on downflow and multipositional furnaces but not usually on upflow furnaces?

The auxiliary limit control is typically found on downflow and multipositional furnaces to enhance safety and operational efficiency. This control acts as an additional safeguard that monitors temperature, preventing overheating by shutting down the system if it becomes too hot. This is particularly important in downflow furnaces, where the airflow pattern may lead to different temperature dynamics compared to upflow designs.

In upflow furnaces, the configuration and airflow pattern often allow other safety features, such as the main limit control, to adequately manage overheating risks. Therefore, while auxiliary limit controls can provide an extra layer of protection in downflow and multipositional setups, they are not generally necessary in upflow furnaces, which have their own protective mechanisms tailored to their design and airflow characteristics.