LOW VOLTAGE WALL MOUNTED THERMOSTATS RK Series ? Heat Only for 24V and Millivolt Systems Wall mount thermostats provide low voltage operation and feature Fahrenheit/Celsius temperature scales. Sealed contacts. Positive off. Thermostats do not contain mercury. No leveling required. 1 amp. 50-90° F temperature range. Measures 3" x 3-1/4" x 1-1/6". UL listed.