Furnaces can be quite complicated parts of the home HVAC system. Knowing a few basic pieces of information regarding how a furnace functions may help you determine what might be contributing to your HVAC woes. Below is a video of the basics of how a furnace functions.

Be Aware: Some furnaces have pilot lights. Some have glowing igniters. The sequence of events for the furnace turning on will be slightly different. The Furnace in the video was a Trane. Here is the general sequence of events that should occur when the furnace turns on:

Basic Furnace Operation

It’s important to note that the specific sequence of events may vary depending on the type of ignition system and the model of furnace you have. It’s always a good idea to refer to the manufacturer’s instructions for your specific furnace when troubleshooting any issues.

1. The thermostat is the control panel for your heating and cooling system. It is usually located on an interior wall of your home and has a temperature dial or digital display. To turn on the furnace, you will need to set the thermostat to “heat” and set the temperature to a level above the current room temperature.
2. Once the thermostat is set, it will send a signal to the furnace to turn on. This signal is usually in the form of an electric current.
3. The furnace control board is a computer that controls the furnace’s operation. It receives the signal from the thermostat and activates the ignition system.
4. The ignition system is responsible for starting the burners, which are the component of the furnace that burn gas to produce heat. There are several types of ignition systems, including pilot lights, electronic ignitions, and hot surface igniters. Whichever type you have, the ignition system will generate a spark or heat to ignite the gas in the burners. Igniters can fail to ignite and will stop the furnace from progressing to subsequent steps. They can be replaced.
5. Once the burners are ignited, they will start heating the air inside the furnace.
6. The blower motor is a fan that circulates the heated air through the furnace and into your home. Some blowers / draft motors start turning to create a draft prior to ignition
7. It will start once the burners are ignited and the furnace is producing heat.
8. A flame sensor ( placed in the path of one of the burners) may also monitor that a proper flame has been established and continues. Without a good flame, the furnace will shut down. Sometimes flame sensors need to be cleaned or replaced if not properly functioning.
9. The furnace control board will continue to monitor the temperature and operation of the furnace and make any necessary adjustments to maintain a consistent temperature. This includes turning the burners and blower motor on and off as needed.

It’s important to note that if any of these components are not functioning properly, the furnace may not turn on or may not operate efficiently. If you are experiencing issues with your furnace, it may be helpful to check each of these components to see if any are the cause of the problem. If you are unable to resolve the issue, it may be necessary to call a professional furnace repair technician for assistance.