If you have a natural gas forced air furnace, this is the programmable thermostat for you. Using Google Home App, you have complete control of this thermostat including voice commands. Does presence sensing to turn down the thermostat when you're gone ... save money. Do it yourself! If you only have a 4 wire system (no common wire) and are willing to give up manual fan control, move the G: Fan (green wire) to the C wire terminal at the furnace and use it. Or buy a 4 to 5 wire converter.