What are the three types of ignition systems?

The correct classification of the three types of ignition systems in HVAC applications includes standing pilot, intermittent pilot, and direct ignition.

A standing pilot system is a continuously burning flame that is used to ignite the gas when the appliance needs to operate. It remains lit whenever the appliance is in use and is a common feature in older heating systems.

An intermittent pilot system, on the other hand, uses a pilot light that ignites only when there is a call for heat, which increases safety and energy efficiency. This type typically uses a spark to light the pilot flame as needed, reducing gas wastage.

Direct ignition systems utilize a device that can ignite the gas burner directly without the use of a pilot flame, often using electronic ignition systems like hot surface ignition or spark ignition. This method enhances efficiency and provides reliable operation.

The other options do not encompass the correct distinctions and combinations of these ignition types. Understanding these three systems is crucial, as they impact the efficiency, safety, and operation of heating appliances in HVAC service.