Hot Topics: Smart Thermostat Compatability

open thermostat panel

The Forum features conversations between more than 250,000 experts and novices about over 120 categories, so each week we highlight a conversation that may help with your next project. This transcript has been lightly edited.

Original Post: Trouble with finding smart thermostat compatibility

noblerare - Member

Hi, I am trying to upgrade our current thermostat to one of the smart thermostat options that the market offers. I have tried going through the Google Nest compatibility checker and the online chat agent tells me that my wires appear to be compatible but my furnace is incompatible.

I have a Trane XV80 central furnace and a Trane XB13 central AC unit. Here is a picture of my current thermostat setup.

open thermostat panel

I've got several questions. First, what does the W/E connection refer to? I know what W and E refer to individually but when actually hooking a smart thermostat, I'm not sure which connection to put the white W/E wire into.

Second, does anyone know why my furnace is incompatible and if there is a smart thermostat option that would work for me?

lawrosa - Super Moderator

you do not have the c wire. You would need to install a power extender kit.

My advice would be get an ecobee if you really want a smart t stat. To me they are just a gimmick..

The t stat needs 24 volts and as said you have no C wire that provides this voltage.

A helpful video about this.

And another.

lawrosa - Super Moderator

But because of that power robbing feature of the power extender kit it takes power from your control board. Robbing it. Boards may tend to fail more often then not. Its my advice to have new t stat wires run and add a separate transformer to power the said smart t stat.

lawrosa - Super Moderator

Last you can get something like this if you don't mind a wire running up the wall to your t stat.

Geochurchi - Member

Hi, any spare conductors in that cable behind the Tstat, hard to tell from the pics, try and pull the cable out of the wall , also check the other end at the furnace, post some pics of the control board at the furnace.

lawrosa - Super Moderator

Yes I see an orange black and blue wire in there. He can get a C wire. Need a pic of the board at the furnace.

I think this is the XV80 board from trane

thermostat electronic board

noblerare - Thread Starter

Here is a picture of the connections at my Trane XV80 furnace. If I were to purchase something like the Ecobee and install the power extension kit which would help me get a C connection, would that work?

thermostat wiring board

lawrosa - Super Moderator

There are extra wires in the wall behind t stat. Pick one and strip it so you have 5 wires.

Then at the furnace board find that extra wire in the t stat wires up there.

Connect that wire to C at the furnace board. When you hook up the t stat hook that wire to C. That should power the t stat and no power extender needed..

Kill power to furnace when working on that board.

lawrosa - Super Moderator

There is a blue black and orange wire in that bundle. Pick one and use it as the c wire.