Which factor does NOT typically affect the life expectancy of a hot surface igniter?

The life expectancy of a hot surface igniter is influenced by several key factors such as material composition, operating voltage, and ambient temperature.

Material composition directly affects how well the igniter withstands the heat and thermal cycling it undergoes during operation. Igniters made of certain materials might deteriorate faster than others, impacting their longevity.

Operating voltage is also crucial because igniters are designed to operate within specific voltage ranges. If the voltage is too high or too low, it can lead to premature failure. Too high a voltage can cause overheating, while too low may not provide sufficient heat for ignition.

Ambient temperature plays a significant role as well. An excessively high ambient temperature can cause thermal stress and degradation of the igniter, while lower temperatures may affect the ignition process but are typically less detrimental than high temperatures.

In contrast, the shape of the igniter does not significantly impact its life expectancy. While it may influence the efficiency of ignition or the thermal distribution, the fundamental material properties and operational conditions are far more influential in determining how long the igniter will function effectively. Therefore, it is not considered a typical factor affecting the life expectancy of a hot surface igniter.