fire box

fire box (plural fire boxes)

1. The hearth of a metal-forging shop; the forge of a smithy.
2. An enclosed hearth with hatch for refueling that is attached to or built into a boiler that supplies steam for mechanical power.

   The brakeman had to help the fireman shovel coal into the firebox as the engineer coaxed his locomotive up grade.

3. The internal hearth of a furnace, stove, or heater.
4. The hearth of an outdoor grill.

   When the bottom of the grill firebox burned through, everybody ran over and stomped embers too keep the picnic shelter from catching fire.