NOTE: If you are replacing a thermostat, be sure to cut power to the board on your furnace that powers the thermostat. I made the mistake of just turning off the breaker labeled ‘AC’. The board still had power. As I was replacing the first thermostat, I must have shorted wires, which is likely to happen to most people. Lucky for me, this simply burned the fuse

I recently purchased and installed 4 IRIS/Radio CT101 thermostats from Amazon. This post is just to document the first part of this adventure: installing the thermostats. There might be some better guides out there, but I’m just wanting to document the things I ran into in the hopes that it might help someone in the future.

NOTE: If you are replacing a thermostat, be sure to cut power to the board on your furnace that powers the thermostat. I made the mistake of just turning off the breaker labeled ‘AC’. The board still had power. As I was replacing the first thermostat, I must have shorted wires, which is likely to happen to most people. Luckily for me, this simply burned the fuse on the board, and it only cost me a few bucks and a trip to the auto store. It could have been much worse. These boards typically have a red LED on them, and at least on mine, you can see the light without opening up the furnace.

First, I want to talk about the reason I went with this thermostat. If you already know what you want, you should probably just skip ahead to the next section. My main reason for this thermostat was the price. $45 x 4 thermostats is a much easier pill to swallow than $250 x 4 for something like a Nest thermostat.

One thing to keep in mind is that the Nest is, by itself, a ‘smart’ thermostat, whereas the CT101 is  a simply a ‘connected’ thermostat. The difference is that a smart thermostat can adjust the temperature on its own based on criteria such as the weather. However, a thermostat such as the CT101 doesn’t really offer much more than a 7-day programmable thermostat, except for the fact that you can connect it to a home automation system such as SmartThings, or like in my case, Home Assistant. But that integration makes it much more powerful than the smart thermostats on the market. You can adjust the temperature in your house based on virtually any information available via the Internet or other sensors in your house.

The CT101 comes with an optional wall plate. I think it looks much better without it, but you may need it if this thermostat is smaller than your old one in order to cover up holes or paint discoloration. It is also a little more difficult to install the wall plate.

One thing that I discovered is that the builder of my house didn’t connect the C-Wire on any of the thermostats. This is a wire that is used to provide power to the thermostat, but isn’t required if the thermostat has batteries. It was annoying to see that my thermostats were capable of using the C-Wire, but the builder just didn’t bother hooking them up, and to make things worse, they actually cut them back. My thermostat had the White(W/Heating), Yellow(Y/Cooling), Red(R/Power), and Green(G/Fan) wires connected. However, I would recommend connecting the C-Wire if you can since these thermostats typically use a lot more power since they need to be communicating regularly.

Fortunately, both ends of the wire, on the thermostat side and the furnace side, had some slack on it. So I was able to pull it out and simply connect the C-Wire on both ends. The pictures below show wires. The first shows the Blue C-Wire connected to the C terminal on the thermostat. The second picture shows the furnace, and I connected that to the C terminal on the furnace board. That’s really all there was to it.

One thing to keep in mind is that you may actually have 2 sets of wires coming into the furnace. One of them go your thermostat, and the other might go outside to control the compressor for your AC. In the second picture, you can see another wire connected on the C terminal and the Y terminal on the furnace. Those wires are going out to the compressor. You don’t need to worry about that for installing the thermostat, but it was something that I learned in this process so I figured I would pass that knowledge on.

Installing the Thermostat
This part is easy, unless you are colorblind. All the terminals are named based on the color of the wire. Yellow goes to Y, white goes to W, and green goes to G. Red is a little different in that there is an Rh and an Rc terminal. For most people, you should be able to connect it to either one since they are bridged together with a small wire. If you have separate wires for Rh and Rc, then you remove that bridge and connect each wire to the corresponding terminal. The only one that doesn’t follow the colors is the C wire. It’s usually blue and it goes to the C terminal.

Heat Pumps
So I had no problems with the 2 thermostats on my main floors(other than frying that fuse). After I connected them, they worked right away. However, the basement did not work at all. After an hour of messing with it and checking the wires, I consulted the manual (remember kids, read the manual first), and discovered the switches in the battery compartment which adjust things like gas, electric, and of course heat pump. From what I have read, other thermostats have settings in the menus to adjust these things. But after I set the switches correctly, everything was working perfectly.

That’s it for this post. As always, post a comment if you have questions. I’m by no means an expert on this, but I will help as best as I can. I hope to have the next post done soon. That one will be way more interesting that this one. I just wanted to document my experience with physically installing the thermostats.

3 Replies to “Installing a Smart/Connected Thermostat

  1. Your article is very useful. Thanks.

    I have a newbee question; What’s the point with having more than one thermostat?

    In my modest understanding of how this works, a thermostat turns on/off a heat source depending on the measured temperature, compared with a boundary. What is the point on having 2 or more thermostats if you only have a single central heater?

    Thank you.

    1. At least in the US, a house will typically have a single thermostat for each floor of the house. This is because warm air rises and the temperature can vary a good bit between floors of the house.

      Even if those house only have on unit, they will have dampers that only send air to one floor. So you need a thermostat on each floor.

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