Be sure to insert your R/Rc/Rh wire in the Rc terminal of your ecobee3 lite thermostat. Fast, easy installation – install your ecobee in 30 minutes or less. The step-by-step guide on our mobile app and free expert support make it easy.Smarter comfort – your ecobee understands your local weather, schedule and desired comfort settings, to ... However, without a G wire, Nest will not be able to control the fan independent of heating. † Common wire (C) not required in most cases, but strongly recommended. ‡ Use Rh or Rc in single transformer systems; no jumper wire required.
Identify the Available R Wires. Check the wiring at your old thermostat to see if it has one or two R wires. If you have one R wire, connect it to RH at the iDevices Thermostat and leave the blue jumper in-place to RC. If you have two R wires, connect RC to RC and R/RH to RH and remove the jumper.
For instance, the Nest Thermostat and the Nest E Thermostat can usually run without a common wire — see below for more information. Other thermostats, like the Ecobee, come with an adapter that can be used if you already have four wires, but no common wire — Ecobee thermostats are also discussed below.