A thermistor is a temperature-sensitive resistor that changes electrical resistance in response to temperature variations, commonly used in HVAC systems to measure indoor and outdoor air temperature. The name combines “thermal” and “resistor,” describing its fundamental operation. Thermistors are cost-effective, respond quickly to temperature changes within 5 to 10 seconds, and are available in negative temperature coefficient (NTC) and positive temperature coefficient (PTC) designs.
Performance Characteristics
NTC thermistors decrease in resistance as temperature increases and provide accuracy within 1 to 2 degrees Fahrenheit across typical HVAC operating ranges of 40 to 100 degrees Fahrenheit. They cost 5 to 20 dollars per unit and have response times faster than mechanical sensors. PTC thermistors increase in resistance with temperature and are used less frequently in HVAC applications but offer self-regulating heat protection.
System Integration
Thermistors connect directly to control boards through 2-wire circuits, reducing installation complexity and material costs. They function reliably in standard HVAC equipment without requiring external power supplies beyond the control system voltage. Their widespread use in residential thermostats and zone sensors makes them the industry standard for temperature measurement in cost-sensitive applications.