What is the main purpose of a fan interlock relay in a heating system?

The main purpose of a fan interlock relay in a heating system is to prevent heating if airflow is insufficient. This safety mechanism ensures that the heating system does not operate unless the blower fan is functioning properly. When the system detects an issue with airflow, such as a blocked vent or malfunctioning fan, the relay will prevent the furnace from igniting. This is crucial because heating systems can pose a fire hazard or lead to equipment damage if they operate without adequate airflow, as the heat exchanger can overheat and degrade. By requiring sufficient airflow before allowing heating to occur, the fan interlock relay protects both the system and the safety of the occupants.