How Does a Furnace Blower Work?

This is a short guide for you to understand just how important the function of your furnace blower is and how it works. The furnace blower’s main function is to draw heat from the furnace and distribute it throughout the house. Below are the parts which play a role in the workings of the blower as well as the steps or events that lead to its activation.

Components of a Modern Furnace

  • The burners
  • Heat exchanger
  • Draft inducer
  • Control and safety devices (i.e. circuit board relays, thermostat, flame sensors, etc.)
  • Blower
  • Venting system

Setting the Thermostat

The thermostat is a switch that, when it is set, will automatically activate and complete a circuit once it detects that the room's temperature has become colder or has dropped below your desired temperature setting.

Initiating the Heat Sequence

This will then start the heat sequence. Once the heat sequence is initiated, the relay in the circuit board will close which in turn powers up the motor of the blower in the furnace.

Starting the Flame

After the motor gets powered up, a flow of electricity is then sent to the ignition system from the igniter relay on the circuit board, making it very hot. The gas valve then gets activated through another electrical current from the circuit board which then allows the gas to flow through to the burners thereby starting a flame. Once the flame has been started, the safety controls and sensors of the furnace will shut the gas down if there is no flame to prevent gas buildup or if the furnace overheats. Either way it is designed to prevent an explosion which is a safety feature of the furnace.

Heating Up

When the flame from the burners goes through the heat exchanger, it then starts heating the walls of the heat exchanger which are made out of metal for the sole purpose of trapping and building up the heat in this chamber until it is hot enough.

Activating the Blower

Once the desired temperature is reached, the furnace blower is then activated via the blower relay in the circuit board.

Spreading the Heat

As a result, air is then forced into the heat exchanger thereby removing the hot air from the metal walls, cooling it down somewhat to about 100-120 degrees Fahrenheit. The warm air is then forced to exit through the venting system, which is a series of air ducts or vents which are spread throughout the space that is to be heated. Modern versions of the venting systems will allow hot air to pass through one main air vent which then goes thru the blower while at the same time drawing the colder air from another main vent back into the furnace for reheating the air which is then blown back out into the home, a feature which allows for more flexibility in the placing of the air vents enabling a wider range of coverage which is especially handy in larger homes.