You can think of a Dual Thermostat as being like two thermostats, in one. Imagine you have two thermostats and each is wired to your furnace with a switch that controls which thermostat your furnace is receiving its commands from at any given time. This has the same result as installing a dual thermostat.
A dual thermostat is capable of having two distinct programs programmed in it. Most commonly a “present” program, which warms up during the day, cools in the evening etc. and an “away” program which simply protects the building from freezing, say holds a constant temperature of 40F inside. The dual thermostat can switch between the two programs when it receives a 12V input, which is accomplished using a 12V power supply and either our FAD2 Freeze Alarm Deluxe or the FGD400 Sensaphone 400. Both of these units can be toggled remotely over the telephone to close the 12V circuit toggling your Dual Thermostat to switch programs.