Even though Ecobee does not require a c-wire, you still need to have a 4-wire thermostat cable because they require a power extender kit. You will connect the wires from your furnace to the power extender kit and then to the thermostat.

Can ecobee be installed without a C wire?

Even though it comes with an adapter for missing c-wires, ecobee is what we'd pick even for systems with a c-wire. If you've got a 24v HVAC system but no C-wire, check out the ecobee product line. Every ecobee ships with an adapter that you can install yourself at your furnace to make up for a missing C-wire.

Does ecobee come with C wire?

Depending on your system, the Power Extender Kit (PEK) included in the box with every ecobee may be able to provide a C wire connection. However, if your system is heat-only or your thermostat controls two separate systems (such as a boiler and air conditioning), the PEK will not be compatible.