This is a function for a heat pump; people who own these systems are very familiar with. It is the infamous “auxiliary heat”. It is well known that when a heat pump runs with the auxiliary heat on it consumes much more power, up to three times more, to be exact, depending on the size of your system. These old thermostats, aka “dumb thermostats”, will not help your power bill. In order to control the auxiliary heat more efficiently, the thermostat has to have the ability to know what the temperature outside is. Once the temperature outside is known, a calculation can be made in order to provide the best comfort for the least amount of energy. Geofencing thermostats in general, in this case, the ecobee and the Nest Thermostat, have the ability to know the temperature inside and outside your home; even more, they know the humidity levels inside your home as well. How do they do this you may ask? It is very simple; they are connected to the Internet through Wi-Fi. An Internet connection allows them to know the temperature, the weather, and everything else necessary to make you comfortable. When it comes to the emergency heat, the problem is: when you have a heat pump, an old thermostat will turn this heat source on when it is not necessary. For example, if you get home and your thermostat is set at 68°F, and you change it to 71°F you will have more than 2°F temperature difference. Your old thermostat will automatically bring the auxiliary heat on even if the temperature outside is warm. This is very counterproductive and wasteful. On the other hand, and it is the case for the ecobee and the Nest Learning Thermostat, you can set them up so the auxiliary heat will not come on unless the temperature outside is below a certain range. For example, you can set up in Nest Thermostat to NOT use the auxiliary heat unless the temperature outside is 40°F or less. If in the whole month of November the temperature outside never drops below 40°F, you will not use the auxiliary heat at all, period. This is actually quite amazing, it is almost like a safety guard for wasting money. Your heat pump should have the ability to heat your house no problem when the weather is relatively warm. These are two common cases for when your auxiliary heat should kick on. It should turn on when the unit goes into what is called a “defrost cycle”. This is when the heat pump must run in the cooling mode in order to heat the coil outside your home in order to get rid of ice buildup. This is something that cannot be controlled by the thermostat, and it is completely normal. The other common case is when the temperature outdoors is really low, and the unit has trouble heating your house. It is important to mention that regardless of the type of thermostat they use at home when it gets extremely cold or hot outside, any system will run for an extended period of time. In other words, you cannot expect to set your smart thermostat at 78°F and expect your unit not to run for a long time, thus increasing your power bill. The tool is almost as good as you are able to use it.