The ERT20TX from SALUS Controls is a stylish and accurate dial thermostat. This thermostat has been specifically designed to be used for both Volt Free and AC heating applications, can replace most common residential thermostats and is designed to be used with electric, gas or oil heating control systems. Unlike ordinary single unit design thermostats, this is a new type of thermostat separating the operational functions into two units. The receiver (sold separately) is used for switching your boiler on and off. The thermostat provides the user interface and temperature sensing / control. The two units are linked together by a Radio Frequency (RF) signal.