Apple HomeKit Compatibility: The Nest Learning Thermostat works with 95% of 24V heating and cooling systems, including gas, electric, forced air, heat pump, radiant, oil, hot water, solar and geothermal. Heating: 1, 2, and 3 stages (W1, W2, W3) Cooling: 1 and 2 stages (Y1, Y2) Heat pump: with auxiliary and emergency heat (O/B, AUX, E) Humidifier or dehumidifier (HUM, DEHUM) Fan (G) Power (C, RH, RC)