In a gas furnace, what might cause inconsistent heating?

Inconsistent heating in a gas furnace is often a result of airflow issues, and a dirty furnace filter or duct obstruction is a prime factor that can lead to this condition. When the furnace filter is clogged with dirt and debris, or if there are obstructions in the ductwork, it restricts the flow of air. This can lead to insufficient airflow through the furnace and into the living spaces, causing uneven heating throughout the home.

As the furnace tries to operate with these airflow restrictions, it may struggle to maintain the set temperature, leading to hot and cold spots in different areas of the house. Clean and unobstructed filters and ducts are essential for optimal furnace performance, ensuring consistent heating and efficient operation.

In contrast, the other options, such as a fully functional gas valve, a properly sized expansion tank, or an updated thermostat, generally relate to the operational efficiency or control of the heating system but do not directly impact the consistency of heating in the same way.