Our top-choice smart thermostats that don`t require a C wire in 2021 are...
(Android Central)

Many of the best smart thermostats require a C wire (`common` wire) to power it due to their LED displays and Wi-Fi-powered advanced functions, leading homeowners with older heating systems to look for smart thermostats without a C wire requirement. If you don`t already have a C wire in your system, these smart thermostats use separate power sources or adapters that let you monitor your home climate without having to hire a professional to rewire your home. Simple and straightforward Nest Thermostat E Staff pick Our top pick for the best smart thermostat without a C wire goes to the Nest Thermostat E. It`s a great option for folks who don`t want to spend too much and prefer minimalist devices. The display simply shows the temperature setting, while the app lets you prioritize certain rooms` cooling, change settings when you`re away, and lets you know if it senses a problem. Most importantly, the Thermostat E features a built-in rechargeable lithium-ion battery that bypasses the...