A:Answer Hi there, Mike. Thanks for your inquiry about the Nest Learning Thermostat. Most 24V heating and cooling systems, including all common fuel types like natural gas, oil, and electricity are compatible with Nest thermostats and would generally work without a common (C) wire. However, there are some systems that would require a C wire on the new Nest Thermostat like a heat only or cool only system. And sometimes, you may need to connect a power accessory like the Nest Power Connector to make your system compatible. Either one will provide a stable power source for your Nest thermostat when your system can’t deliver enough consistent power to it. We recommend checking your system’s compatibility with our online Compatibility Checker: https://store.google.com/intl/us/widget/compatibility/thermostat/
