A:Answer Nest Thermostat works with most 2-wire, 24V heating and cooling systems, including furnaces, air conditioners, boilers, and heat pumps with either forced air or radiant delivery. We suggest using our online compatibility checker first to ensure that your system is compatible with Nest Thermostat. Here’s the link: https://store.google.com/us/widget/compatibility/thermostat
Typically, smart thermostats don’t require a common (C) wire, but every system is different. Without a common wire, your Nest thermostat will charge itself through power sharing using your existing heating and cooling wires. However, when your heating and cooling wires are not able to deliver the needed power for your Nest thermostat, you may need to connect a common or C wire since it helps deliver enough consistent power to your thermostat.
When there’s a C wire, it becomes the thermostat’s go-to for power backup when power sharing doesn’t work. This can also conserve battery life since the batteries will likely only be in use when there’s a power loss to the thermostat.
Also, Nest Thermostat (2020) has a backup battery. For systems that are not using a C wire, the average battery life is three to six months. However, depending on the Wi-Fi activity on the thermostat, it may be possible to extend or reduce the battery life.
For further assistance, you can contact our support team here anytime: https://support.google.com/googlenest/gethelp
