Which control is commonly found on downflow and multipositional furnaces?

The auxiliary limit control is commonly found on downflow and multipositional furnaces because it serves a critical safety function by monitoring the temperature within the furnace's heat exchanger. If temperatures exceed a certain threshold, the auxiliary limit control will shut down the system to prevent overheating, thereby ensuring safe operation of the furnace. This control helps protect the furnace from potential damage and minimizes the risk of fire hazards.

In downflow and multiposition applications, where the airflow direction can change depending on the installation configuration, having an effective limit control is especially important. It provides an additional layer of protection, complementing other safety features that regulate the heating operation.

While other controls are important in different contexts (like flame roll-out control that specifically deals with issues related to the combustion process), the auxiliary limit control directly relates to the operation and safety of downflow and multipositional furnaces, making it the more relevant choice in this scenario.