Step 1: Drawing Cool Air Into The Furnace

• Diagram Of An Electric Furnace
  
  At the base of an electric furnace is a powerful, motorized fan that pulls air out of the building's interior and pushes it into the electric heating coils. To keep the sensitive motor free from dust particles (and to keep impurities from burning up in the heating coil, causing unpleasant odors), the furnace's air intake opening is covered by a special filter that traps dust, dirt, mold and other potential threats to the machinery.
  
  

Step 2: Heating The Air

• As most furnaces are located in the basement, the furnace's fan pushes air directly upwards to aid in spreading the heated air throughout the rest of the building. The quickly-moving air passes through three layers of red-hot electrical coils.
  
  In electrical engineering, certain materials (and shapes thereof) can cause resistance against the flow of electricity. In some cases, this energy lost to resistance performs work (e.g. computers boot, motors turn, etc.). However, if a metal wire is tightly coiled, the electrical resistance is converted directly into thermal/heat energy. When exposed to these electrical-resistance-heated coils, air molecules with automatically absorb this thermal energy, which increases air temperature.
  
  Just an electric hair dryer heats air with several rings of coils and blows it in a focused direction, an electric furnace pushes air through three layers of hot metal coils. This increases the air's temperature considerably before propelling it into an outlet pipe that branches to vents throughout the building.
  
  

Step 3: Recirculation And Feedback Control

• The average volume of a building is many, many times the air intake rate for an electric furnace. Likewise, the temperature for air leaving the furnace cannot be too high, lest it become uncomfortable or even a fire hazard. To compromise, electric furnaces are controlled by an electronic thermostat. Based on the target temperature and the size of the building, the thermostat is programmed to limit how long the furnace runs, how fast the motor goes and how hot the coils are.
  
  Electric furnaces raise ambient air temperature by recirculating heated air, incrementally adding temperature each time. Plus, because warm air has higher pressure than cool air, cooler air naturally sinks to the basement, where the furnace is waiting to suck it up and heat it. If this newly- heated air is even hotter than the aforementioned "warm air," the warm air will then sink below to the furnace for additional heating.
  
  Meanwhile, the thermostat has built-in functions to judge how much thermal energy needs to be transferred into the air. This way, the furnace shuts off sooner, preventing and/or temperatures higher than expected.