Which component directly controls gas flow in a gas furnace?

The component that directly controls gas flow in a gas furnace is the gas valve. This device regulates the amount of natural gas or propane that enters the furnace for combustion. When the thermostat calls for heat, it signals the gas valve to open, allowing gas to flow to the burners where it can be ignited. The precise control of gas flow is essential for the furnace to operate efficiently and safely, ensuring that there is the correct air-to-fuel ratio for optimal combustion.

The furnace blower, while an important part of the system, is primarily responsible for circulating the heated air throughout the home rather than controlling fuel flow. The draft inducer fan helps to create a proper draft for venting exhaust gases and ensuring that enough air is supplied for combustion, but it does not regulate the gas supply itself. The heat exchanger is crucial for transferring heat from the combustion process to the air that is circulated but does not play a role in gas flow regulation.