Lessons Learned for Installing a Smart Thermostat

Are you a DIY’er? 

If so maybe you’ve been thinking of installing a Smart Thermostat into your home. Well I have been there and done that a few times now and I can share some lessons I learned that might save you some time and frustration. 

Installing a Smart Thermostat is different than installing any other IoT (Internet of Things) or "Smart" device; which is a fancy way of saying it will connect to your WiFi and the Internet. With most Smart devices it’s a matter of downloading an app to your Smart Phone and connecting the device to your WiFi. For Smart Thermostats, however, you’ll need to understand the fundamentals of thermostat wiring and, in particular, what a C-wire is.

The good news is most furnaces and gas stoves that already have a thermostat can be controlled by a Smart Thermostat. The bad news is most do not have a C-wire coming from the furnace to the thermostat. 

The C-wire provides a constant 24-volts of power to the Smart Thermostat; which most require to function. Many legacy thermostats are battery powered. The picture below shows a legacy thermostat’s terminal plate with no C-wire or C-wire terminal. Not to worry, the Smart Thermostat terminal plate will have a C-wire terminal. You will just need to install and connect a C-wire adapter as the last piece of the puzzle.

All of this wire talk begs the question: what are the other wires for? Well here is the usual standard schematic to help you get an understanding:

• Blue or Black (usually) – The Common C-Wire (a.k.a.Common Wire) that provides steady 24VAC.
• White The white wire connects to your heat.
• Yellow The yellow wire connects to your cooling.
• Green The green wire connects to the fan.
• Orange This wire connects to your heat pump (if applicable).
• Red (C) The Rc wire connects to the cooling system.
• Red (H) The Rh wire connects to the heating system. This wire may be red without an “H” attached, in some cases.

Take some pictures of the old thermostat for reference before removing wires. Generally the wiring of the new Smart Thermostat will be straight forward and similar: W to W, G to G, RH to RH and so on. But don’t start wiring the new Smart Thermostat until after you install the C-wire adapter - if applicable. Oh, and turn off any power at the breaker box that might be going to the thermostat. 

C-wire adapters can be bought online from several web sites. The two wires from a C-wire adapter will be wired into the C and RC (ground) terminals on the Smart Thermostat, as illustrated below.

Once the C-wire adapter wire has been installed and connected to the terminal plate the other wires can be connected. Make sure they are all connected firmly before installing the Smart Thermostat onto the terminal plate.

That should do the trick. Turn back on the power and the Smart Thermostat should boot up. Immediately test to make sure the furnace and\or Air Conditioning is responsive. Smart Thermostats have configuration menus explained in the manuals and sometimes the default settings are not correct for communicating with your furnace or AC unit.