because it calculates how long it takes to get to a desired a temperature (esp for me with radiators in my house), my heat costs have been cut drastically. A lot of people will turn down the temp on their thermostat thinking it will make it cooler faster or the other way to make it warmer faster. The nest helps prevent that. Since it learns your habits and can set an auto schedule (if you dont want to set one manually) it will have the desired temp at the desired time instead of only turning on at the time you set, like other thermostats. I have 2 of these in my house, and I highly recommend them. I have seen drastic improvements, esp in the summer with my A/C system.