The wiring to my existing thermostat is as follows:

W — White

Y — Blue

G — Green

Rc/Rh — Red

The problem with this wiring is that it doesn’t include a “common” wire.  It could have been run but it isn’t necessary for this thermostat (which is battery powered).  The common is the back side of the AC transformer, which is needed to power the thermostat.  The thermostat cabling that was run to my thermostat only had four wires so I was forced to run another wire.  Luckily my furnace is straight below my thermostat and I was able to run a fish up from the furnace room to the hole in the wall and pull a wire down to the furnace.  I didn’t have any thermostat wire so I just ran some random alarm wire and twisted all four conductors together.  You should have 18 gauge wire for thermostats and this put me above that.

In order to connect to the common on my furnace I had to first remove the top (front) cover to the furnace.  You should shut off your furnace before you open it up.  You can see the light switch on the right of my furnace which shuts it off.  I didn’t actually shut mine off when I wired it up because all the wires we’ll be working with are low voltage (28 VAC).  Both covers “hang” from the top lip of the cover so you must remove the top one first to be able to get the bottom one off.

With both covers removed (and the control board circled in red):

Here I have drawn a red box around the control board

I ran my extra wire along the existing thermostat wire, in the hole in the side…

Locate the control board (where all the wires go) and look for the thermostat wires (Red, Green, White, Blue).  There will be a connection labeled with a C or Com or Common:

There may be something connected to the Common terminal already (in my case our humidifier is wired to the common already).  You should be able to connect your new thermostat common wire in addition to what is already there.  Once you have this end tied up, reinstall the covers and go back to the thermostat end.Make sure you take good notes as to how your current thermostat is wired.  I always take a picture as well.  Wiring the Ecobee in this case was really straight forward as far as the abbreviations compare.  Here is how it works out:

I’ll leave the mounting of the physical mounting of the thermostat to you (I used the two wall anchors they provided with the thermostat).  Here’s what the base plate looks like all wired up:

Ecobee EB-SmartSi-01 mounting plate all wired up

Once you have it all wired up, push the wires back into the hole as much as you can because there isn’t a lot of extra room.  Snap on the thermostat and hopefully, if you have it wired up correctly, it will boot right up:

Ecobee EB-SmartSi-01 booting up

The first thing you’ll want to do is connect it to your wireless network.

Connecting the Ecobee to your wireless network:

1. Press Menu button
2. Scroll down to settings and press OK
3. Scroll down to Wifi and press OK
4. Scroll down to your wireless network and press OK
5. Enter your password and wait for it to connect and register
6. Go to the ecobee.com website and create an account and follow their instructions.

Changing the thermostat to 2-stage (if applicable):

1. Press the menu button until you see “Main” at the top of the screen
2. Scroll down to “Settings” and press the center OK button
3. Scroll down to “Installation Settings” and press OK
4. Press OK to select the top item, “Equipment”
5. Scroll down to “Furnace” and press OK
6. Scroll down to “Heat Stages” and press OK
7. Scroll down to “2 Stages” and press OK
8. Repeat steps 1-5 and then pick AC instead to change the cooling stage #

If you have electric heat follow these steps to change it from gas to electric.  I guess the main difference is the timing when the fan runs in regard to when the heating elements heat up.

Changing the thermostat to electric heat (or boiler):

1. Press the menu button until you see “Main” at the top of the screen
2. Scroll down to “Settings” and press the center OK button
3. Scroll down to “Installation Settings” and press OK
4. Press OK to select the top item, “Equipment”
5. Scroll down to “Furnace” and press OK
6. Select “Furnace Type” and press OK
7. Scroll down to Electric (or Boiler) and press OK

Enjoy your wireless “smart” thermostat.

My Other Thermostat Posts:

• How to Program a Robertshaw 9615 Thermostat
• How to Program a Ritetemp Model 8050 Thermostat
• How to Wire an Ecobee EB-SmartSi-01 Thermostat to a Carrier 58PAV Furnace (this post)
• How to Program a Honeywell Thermostat Model T8112D1021