A recuperative melter is a unit melter equipped with a recuperator. Typically, the recuperator is a metallic shell-and-tube-style heat exchanger that preheats the combustion air to 540 to 760°C. The furnace is fired with 4 to 20 individual burners. These furnaces range in size from as large as 250 t per day of glass to as small as 18 t per day of glass. These furnaces are common in fiberglass production but can also be used to produce frit. Some recuperative furnaces are used in the container industry, though this is not common. Furnace life is a function of glass type being produced. For example, a 6-year furnace life is typical for wool fiberglass. A typical recuperative melter is shown in the following figure.