HVAC DIY Tips & Tricks

The Key Components of a Gas Furnace

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Discover the essential parts that make up a gas furnace and learn how they work together to keep your home warm and efficient.  Don't miss out on this informative guide!

What are the Components of a Furnace?

The main parts include a gas valve, heat exchanger, burner assembly, flame sensor, pilot light, blower assembly, control board, and draft inducer motor.

Pilot Light

Pilot lights are used to light the propane or natural gas after it travels through the burners and before it enters the heat exchanger.


The thermocouple senses heat from the pilot light’s flame and sends a signal to the gas valve or circuit board to let it know that the flame is successfully lit.

Hot Surface Ignitor

A hot surface ignitor (HSI) is used in place of a pilot light. electrical current passes through it until it glows bright orange and are hot enough to light the gas as it enters the heat exchanger

Flame Sensor

The flame sensor is a safety device that replaces the older thermocouple. Flame sensors detect heat from combustion and send a signal back to the circuit board, letting it know to keep the gas flowing.

Gas Valve

The gas valve controls lets the gas flow through to the burner assembly and regulates the gas pressure, usually to 3.5 inches of water column (WC).

Gas Burners

The heat exchanger is formed from metal and is designed to direct gas flow while mixing it with combustion air. The gas burner is located between the gas valve and the heat exchanger.

Heat Exchanger

The heat exchanger is what transfers heat from the flame to the air that warms your home. As the flame flows through the exchanger, it turns into toxic fumes that are then exhausted.

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