ventilating-grate

from The Century Dictionary.

• noun An open fireplace, stove, or heater having double walls at the back and sides, with an open hearth or basket-grate for wood or coal. The space between the walls of the stove is open above and below. When in use the air in this space becomes heated, expands, and escapes at the top into the room, fresh cold air entering continuously below, with a great economy of the heat of the fire.