NATE Gas & Oil Forced-Air and Hot-Water Heating Systems Practice Test 2026 – The Comprehensive All-in-One Guide to Exam Success!

A dirty air filter is a common cause of low airflow through a furnace. When the air filter becomes clogged with dust, dirt, and other debris, it restricts the flow of air into the furnace and throughout the heating system. This restriction reduces the overall efficiency of the system, making it work harder to produce heat while limiting the heated air that can circulate through the home.

In a forced-air heating system, sufficient airflow is crucial for optimal operation. If the airflow is low, it can lead to uneven heating, longer run times for the furnace, and increased energy consumption. Additionally, prolonged operation under these conditions can cause overheating and potentially lead to system damage.

Maintaining a clean and unobstructed air filter is essential for ensuring that a furnace operates efficiently and effectively. Regular inspection and replacement of the air filter based on usage and the manufacturer's recommendations are important steps in preventive maintenance for a heating system.