In many countries, it is necessary that people have a way to stay warm. Most people today do not use open flames to heat their homes, instead, due to advances in technology, most homes are heated by a furnace of some type (there are several). However, home heating is not the only use these machines have; furnaces and allied equipment are also used extensively in the metallurgy industry.

Though home heating furnaces, called boilers or heaters in some countries, come in several different types, they all operate on the same basic principle; some type of combustible material is ignited and the resulting heat is moved through the home. The most common type of heater is the natural gas forced air furnace; natural gas is ignited by an electrical spark and the heat is forced out of the duct work by an electric fan or blower. A thermostat allows the heater maintains the desired temperature; when the thermostat reaches the selected temperature, a switch inside of the furnace shuts the fan off, which stops the heat from being distributed through the home.

The other most common type of furnaces and allied equipment are used in the metallurgy industry; unlike home heaters, these furnaces are very large and are capable of reaching very high heats. Smelting furnaces are used for melting metal in order to either change the composition of the material (i.e. reducing iron ore to pig or) or to make the metal more workable, which is vital to many in the manufacturing industry.