Skip to content NREL Buildings Research National Renewable Energy Laboratory (NREL)
Field Test Best Practices: A Resource for Practical Residential Building Science

Main menu

Thermistors

Thermistors are devices in which electrical resistance changes with temperature. Resistance is readily measured by providing a known excitation voltage and measuring the current flow (usually by sensing the voltage drop across a separate known resistance). The usable temperature range of most thermistors is less than that of thermocouples, with a typical range being about -110 to 300°F (-80 to 150°C).

The high sensitivity of thermistors makes them less susceptible to noise-induced errors. Thermistors can be useful for measuring small temperature differences, and for use with data acquisition equipment that does not have a good ability to measure millivolt signals. Thermistors, like other temperature sensors, are available in a wide variety of packages appropriate to various measurement requirements.

Since thermistors dissipate power when energized, they are susceptible to self-heating errors. This error is influenced by the ability of the surrounding fluid to carry away the heat produced. Thermistor manufacturers can provide information on the effect of self-heating in various fluid environments. A common approach to reducing self-heating is to energize thermistors only briefly before making a measurement.

Thermistors come in a number of varieties. They are commonly specified by the nominal resistance at 25 C (77°F), e.g. a "10K Ohm" thermistor will have a resistance of about 10,000 Ohms at 25°C. There are variations in thermistor types even within a single nominal resistance category, (due to chemical "mix"), and users should be sure to obtain the resistance versus temperature table or curve for the particular device purchased.