If you're going from an older thermostat to a new smart one, you may find that ... This one doesn't need a C wire, though I have read about some ...Choose a thermostat that doesn't require a C-wire or an adapter ... The Lux Geo WiFi Thermostat is my favorite recommendation to homeowners ...If you don't have a common wire and want to install a smart thermostat, you still have quite a few options. Option 1 is to buy a smart thermostat that doesn't require a C wire. The Sensi and Ecobee are two top models that don't require a common wire.