What are Parts of a Furnace System for Homeowners to Know?

You know your furnace keeps your Montgomery, AL home when outdoor temperatures drop – but do you know how it operates? There are many parts of a furnace system that function together to create heat and deliver it to your indoor living areas. Our knowledgeable HVAC techs share basic furnace vocabulary to help you become more familiar with the parts of a furnace system.

Parts of a Furnace System

There are numerous parts of a furnace system that work together to create heat and deliver it to your indoor spaces. 

Pilot light

In older furnaces, the pilot light burns constantly, ready to ignite the gas when the furnace turns on to start the heating process.


The thermocouple detects a lit pilot light. When the thermocouple senses a lit pilot light, it sends an electrical signal to the gas valve, signaling it to open for gas flow.

Hot surface ignitor

A newer technology, hot surface ignitors replace pilot lights in newer furnace models. Electrical current is passed through the ignitor, raising its temperature to start combustion when the gas supply turns on.

Flame sensor

The flame sensor is a safety device that detects heat from the hot surface ignitor. If no heat is detected, this device turns off the gas supply.

Gas valve

The gas valve adjusts the pressure of natural gas coming into your home, so it is appropriate for use in the furnace. It also controls the gas to the furnace.


A furnace’s burners mix gas and air to make a flame, which is the furnace’s heat source.

Heat exchanger

The heat exchanger holds toxic gases created when fuel burns. Gases are safely vented away from your home while the heat exchanger gives off heat to the surrounding air. This component looks like a collection of long, metal tubing.

Draft inducer motor

The draft inducer motor starts before gas begins to burn in the furnace. Its job is to help push toxic combustion fumes out of your home’s vent pipe by creating a vacuum.

Pressure switch

The pressure switch ensures the draft inducer motor is turned on to push fumes through the vent pipe. The vacuum created by the draft inducer motor pulls at the pressure switch’s diaphragm to activate it and allow gas flow – if the vacuum is not sensed by the pressure switch, gas is not allowed into the furnace.

Blower motor

The blower motor’s job is to push warm air created by the furnace through the duct system and into the home.

Blower motor capacitor

This component starts the blower motor, and some keep the blower motor running at a consistent speed.

Limit switch

The limit switch detects temperatures within the furnace. If the furnace is too hot, the limit switch turns off the gas to prevent safety issues.

How Do the Parts of a Furnace System Work?

Now that you know the parts of a furnace system, we walk you through a high-level look at how it works. Furnaces offer forced-air heating – they transfer created heat to the air, then send into your living areas. 

Here’s how the parts of a furnace work together to deliver your heat in a gas system:

  1. The pilot light or ignition system lights the burners within the combustion chamber.
  2. The burners burn fuel to create heat.
  3. Heat enters the heat exchanger, where it transfers to air, bringing it up to the temperature set by your thermostat.
  4. Once air reaches the desired temperature, the blower forces the air through your home’s ductwork.
  5. The warm air exits vents and enters your living spaces.

How an electric furnace works

In an electric furnace, there are no gas burners or pilot lights. Instead, the electrical ignition system activates the furnace’s heating elements. As electrical current moves through these coiled heating elements, the air absorbs the heat. Then, the blower moves the heated air through ducts and into your living areas.

Get Furnace Help from Hans Heating and Air!

If any parts of a furnace system are not properly functioning, your heating system is unable to provide efficient and consistent heat for your home. Hans Heating and Air helps Montgomery homeowners with quick and reliable furnace repairs

Ready to upgrade to a more efficient and reliable furnace or heat pump? We offer finance options for customers to enjoy greater comfort and lower utility bills. 

Contact us today to eliminate furnace troubles and regain comfort indoors!

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