Which component of a gas furnace is responsible for igniting the gas?

The ignitor is the critical component responsible for igniting the gas in a gas furnace. It functions by creating a spark or a hot surface that ignites the gas once it is released into the combustion chamber. This ignition process is essential for the furnace to produce heat, as it requires the gas to be lit before combustion can occur.

In many modern systems, ignitors can take various forms, including electronic ignitors or hot surface ignitors, which are designed to enhance safety and efficiency. The ignitor's function is vital because it ensures that the gas flame is reliably ignited when needed, allowing the heating cycle to begin effectively.

While other components like the flame sensor, thermostat, and combustion chamber play significant roles in the operation of a gas furnace, they do not directly initiate the ignition of the gas. The flame sensor detects the presence of a flame to ensure safe operation, the thermostat regulates the temperature by signaling when the furnace needs to heat the space, and the combustion chamber is the area where combustion occurs but does not ignite the gas itself. Hence, the ignitor is the correct answer for its specific role in the ignition process.