A furnace, abbreviated as FURN, is a heating system or device that is used to generate heat by burning fuel or using electricity.  Furnaces are commonly used in residential, commercial, and industrial applications to provide warmth or to melt materials, among other uses.  In a typical furnace, fuel (such as natural gas, oil, or coal) or electricity is used to heat air or water, which is then circulated through a building or process to provide heat.  Furnaces can be classified based on the type of fuel they use or the way in which heat is transferred, such as radiant heating or forced air heating.

Furnaces are also used in industrial applications such as steel production, where they are used to melt metals or other materials at high temperatures.  In these applications, furnaces can operate at extremely high temperatures and may be fueled by natural gas, coal, or electricity.  Furnaces require regular maintenance and safety checks to ensure they operate efficiently and safely.  Modern furnaces are often equipped with safety features such as automatic shut-off valves and sensors to detect gas leaks or other hazards.

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Furnace Design Classification

Electric Furnace  -  This furnace has a heating chamber with electricity as the heat source for achieving very high temperatures to melt and alloy metals and refractories.  The electricity has no electrochemical effect on the metal but simply heats it.

• Arc Furnace  -  A type of electric furnace in which heat is generated by an arc between carbon electrodes above the surface of the material (commonly a metal) being heated.
  
  • AC Arc Furnace  -  A type of electric furnace in which heat is generated by an AC arc between carbon electrodes.
  • DC Arc Furnace  -  A type of electric furnace in which heat is generated by a DC arc between carbon electrodes.
  • Submerged Arc Furnace  -  The SAF uses the arc heat at the end of the electrode and the resistance heat of the charge or slag to convert electrical energy into heat energy so that use elements such as metals are reduced from ores or oxides.
• Induction Furnace  -  Has a coil carrying alternating electric current surrounds the container or chamber of metal.  Eddy currents are induced in the metal (charge), the circulation of these currents producing extremely high temperatures for melting the metals and for making alloys of exact composition.
  
  • Coreless Furnace  -  A type of induction furnace that uses a magnetic field to heat metal objects.  The magnetic field is created by the use of an electric coil, which has a high frequency alternating current passed through it.  The electric coil is placed inside the induction heating chamber and the metal object to be heated is placed on top of it.  There are no coils or cores that generate heat by passing electricity through them.
  • Mains Frequency Furnace  -
    • Chennel Furnace  -  Basically consists of a tiltable furnace vessel with refractory lining onto which single or multiple inductors are mounted.  The melt in this furnace is guided in a closed or open channel.
• Resistance Furnace  -  The heat is developed by the passage of current through a suitable internal resistance that may be the charge itself.  Electric energy is converted into heat when a current flows through the heating element.  The heat is transmitted to the material to be heated by conduction, convection, or radiation.

Fuel Fired Furnace  -  Fired process furnaces have the same function as electric process heaters, which is to heat a fluid to a desired working temperature.  The fluid flows through tubes that are heated by a combusting fuel.

• Coal Fired Furnace  -
  • Cupola Furnace  -  This furnace is used mainly for the manufacture of different grades of bronze and cast iron in foundry processes.  Similar to the blast furnace, the cupola is a refractory-lined steel stack, resting on a cast-iron base plate with four steel legs. The bottom of the cupola furnace has two hinged doors supported in the closed position.
  • Pit Furnace  -  A type of furnace formed like a pit and is used for melting quantities of ferrous and non ferrous metals for production of castings.  They are preferable when work pieces are very long and need to hang vertically to minimize distortion during heating, or for very large loads which are best handled with an overhead crane.
  • Rotary Furnace  -  Rotary furnaces are often used for the heat treatment of bulk materials.  All  materials are uniformly exposed to the heating because their position within the bulk material changes constantly.  A continuous material movement through the heated space can be achieved by slightly and adjustably tilting the rotary furnace.
• Gas Fired Furnace  -  Gas furnaces burn gas to produce heat for a variety of industrial processes.  An enclosed space contains the gas until it reaches the temperature for the application.  Gas furnaces can contain air, oxidized gas, inert gas, reducing, salt bath, or vacuum atmospheres.  Natural gas is the main type of gas used for gas furnaces.
• Oil Fired Furnace  -  Liquid fuels produce combustible fumes.  The majority of liquid fuels are made from fossil fuels, with other variations being hydrogen, ethanol, and biodiesel. Oil is the most common type of liquid fuel used to heat and reheat materials for treatments.  The efficient operation of a liquid-fueled furnace means complete combustion of the fuel without any residue.