Lucifer Furnaces Inc. designed and built a heat-treating box furnace for use with inert atmosphere for stress relief of springs under nitrogen atmosphere. It will be used as an addition to an existing Lucifer Furnace at a facility to reduce the residual stress from manufacturing. Stress relieving reduces the internal stress from manufacturing and increases the mechanical strength of the spring. The furnace has a working chamber measuring 12 inches high x 12 inches wide x 36 inches long and heats up to 2100°F (1149°C) with 15 kW power. It is fabricated with 2.5 inches of insulating firebrick and 2.5 inches of mineral-wool insulating block for superior thermal efficiency. The workload is supported by a 1-inch-thick hearth plate that protects the floor insulation and provides a flat work surface.