What output voltage is required from an oil furnace ignition transformer?

Oil furnace ignition transformers commonly provide 8 kV to 12 kV AC at the secondary. This range is designed to produce a strong spark across the ignition electrode gap under real world conditions such as cold starts, humidity, and airflow variation. Some systems may be specified at 10 kV nominal. The required value depends on burner design and electrode spacing. The transformer must also deliver stable output under intermittent or continuous duty depending on the control system.