What do controls for furnaces and duct heaters check for before energizing heating elements?

The controls for furnaces and duct heaters prioritize airflow checks before energizing the heating elements because ensuring adequate airflow is critical for safe and efficient operation. If the system attempts to heat without proper airflow, it risks overheating, which could lead to equipment damage or create unsafe conditions, such as combustion issues in gas appliances.

Airflow sensors or pressure switches are often utilized to verify that air is moving through the system as intended. This prevents the heating elements from turning on if there is insufficient airflow, ensuring that the unit operates within safe limits and enhances overall system reliability.

Gas pressure, voltage levels, and temperature are also important factors in the operation of heating systems; however, their verification typically occurs post-airflow check. If there’s no airflow, the system won't operate safely, regardless of gas pressure or voltage levels being correct. Therefore, ensuring airflow is the first priority in furnace and duct heater control sequences.