Fuel Savings is idea of this circuit.
The 24 volt source is from the furnace transformer and the 5 ohm resistor represents the furnace gas valve.
Two adjustable resistors are the two Thermostats. One could be set for Day temperature and second thermostat is Night temperature setting.
The bottom right is timer circuit at line voltage. Turn On or Off the SPST switch to simulate the timer adding or turning off the higher set thermostat.
