Before the burner ignites, what is the minimum number of furnace volume air changes required by the purge cycle?

For burner safety and efficiency, the purge cycle is essential before ignition. The minimum requirement for furnace volume air changes during this purge cycle is set to ensure any unburned gas or flammable vapors are cleared from the combustion chamber. The requirement of four complete air changes helps to ensure that the atmosphere within the furnace is safe and free from potentially hazardous materials before the igniting process begins.

This number of air changes allows for sufficient dilution and replacement of the existing atmosphere, mitigating the risk of explosion or improper combustion. The four air changes help to create a stable and safer environment, which is critical to the operation of the burner once ignition occurs.