Furnace firing arrangement nomenclature: If the flame is generated beneath the hearth and then sweeps upward into the heating chamber, what is this furnace configuration called?

Introduction / Context:
Furnaces are often described by how the flame and hot gases are introduced and flow relative to the hearth and charge. This naming helps communicate burner placement, flame direction, and expected heat transfer patterns.

Given Data / Assumptions:

• Flame originates beneath the hearth structure.
• Combustion products sweep upward into the main heating space.
• Standard terminology used in furnace practice.

Concept / Approach:
When primary combustion occurs below the hearth and gases rise into the chamber, the arrangement is termed “underfired.” Sidefired furnaces have burners entering laterally; “covered” is not a standard flow designation; “recirculating” describes flow behaviour but not burner placement.

Step-by-Step Solution:

Verification / Alternative check:
Classic reheating and soaking pit nomenclature aligns with this definition in training materials and OEM docs.

Why Other Options Are Wrong:

Common Pitfalls:
Using operational flow descriptors (like recirculation) as if they were standard furnace configuration names.

Final Answer:
underfired