The Thermostat Probe is installed under the flooring surface and connects to nVent NUHEAT thermostats. It is included with all nVent NUHEAT thermostats and provides a temperature reading of the floor. Our floor heating sensor probes 10 kilo-ohm resistance sensors and the two wires of the sensor are 22AWG. The standard length of the sensor wire is 15 feet. They are included in the boxes of all of our models of thermostats.