A fuel oil furnace ignition transformer steps up line voltage to a high secondary voltage, typically several kilovolts, to create a spark across ignition electrodes. That spark ignites the atomized fuel oil in the burner, initiating stable combustion. The transformer is designed for intermittent high voltage duty, robust insulation, and reliable spark energy even when conditions are less than ideal, such as cold starts or slightly fouled electrodes. Modern systems may use electronic igniters, but classic ignition transformers remain common due to simplicity, ruggedness, and strong ignition performance in many burner designs.
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