It is not clear how high of a temperature that the heat sensor would need to survive and still be able to operate normally in the 90°F-120°F temperature range subsequent to that exposure.
In the range of temperature given, you can likely accomplish the temperature measurement with any of the common electronic temperature sensing types, RTD, Thermistor, Thermocouple, IC sensor.
Protection from dirt and grease is probably best accomplished in a stainless steel case, with or without an integral mounting thread.
The particular choice of sensor may be determined by the interlock instrument that actually controls the exhaust fan.
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