If you are trying to figure out how to connect Nest thermostat wires or an Ecobee in your American home, you probably just took off your old thermostat and found a confusing mess of colored wires. You might be searching Google for things like "what do thermostat wire colors mean" or "where does the blue wire go on a smart thermostat." The truth is, guessing based on wire colors can easily damage your HVAC system. Instead of guessing, there is now a completely free and simple way to identify thermostat wires by photo . Meet thermostatwires.com , a smart AI tool built specifically for US homes that tells you exactly where every wire goes. What Do Thermostat Wire Colors Mean? In a perfect world, every US home would follow the exact same rules. The standard thermostat wire color code goes like this: Red wire (R or Rh/Rc): Delivers 24 volts of power from your HVAC system. White wire (W): Controls the heating system (furnace or heat pump). Yellow wire (Y): Turns on t...