Ecobee Smart Si vs. Ecobee4: Which Should You Buy?

Ecobee has been in the smart thermostat market for a long time. It is currently dominating the space with Ecobee4, but it has also produced several noteworthy products in the past. One of these earlier models is the Ecobee Smart Si. How does the Ecobee Smart Si compare with the Ecobee4?

Ecobee Smart Si

When it first came out in 2012, very few smart thermostats could compete with Ecobee Smart Si. The Wi-Fi connected smart thermostat helped save up to 23% of heating and cooling costs, and it came with a variety of features that made people take notice.

Features of the Ecobee Smart Si

  • Smart. The Wi-Fi connected thermostat knows when to turn your heating or cooling on or off, using algorithms on a variety of information that it gathered from its sensors.
  • Mobile app. The Smart Si was one of the first thermostats that you can control using a mobile device, smartphone, tablet, or desktop computer.
  • Hardwired. The Ecobee Smart Si is hardwired, ensuring that the thermostat had a reliable source of power.
  • Compatible with most homes. The thermostat also promises easy installation, being compatible with 95% of all American homes.

What you would like about the Ecobee Smart Si

Unlike other smart thermostats during its launch, the Smart Si looks sleek and modern. Not only did it come with a minimalistic appearance that is far from the utilitarian look of old thermostat panels, it also comes with a full-color LCD display. It has a navigation pad that helps users switch from one screen to the next as well as set their preferred temperatures. The 2.5-inch display features a resolution of 320 pixels by 240 pixels.

But more than the looks, what made the Ecobee Smart Si a top thermostat during its time was the smarts. It has a web portal that can gather data from different places and figure out how to save you more money, while also automatically adjusting your thermostat. You program the thermostat the way you want it and the system will figure out if it’s too hot outside so it would turn on the cooling more than you intended, or if it’s colder than usual so it would give your room more heat than usual.

The Smart Si also presents several reports that would give you great insights into your cooling and heating behavior. The IQ reports will tell you more about your system, how long your HVAC was running, how the thermostat worked as compared to your set schedule, how the weather outside impacted on your cooling and heating costs, and other data.

Other things you would like about the Ecobee Smart Si includes:

  • Free cooling: switching off the air conditioning and drawing in cool air from outside
  • No monthly service charges
  • Free software upgrades
  • Interactive compatibility checker: lets you know if the thermostat would work at your home before you buy.

What could be better

The Ecobee Smart Si does not have motion and light sensors that would let it know whether you are home or not. This prevents it from turning down the heating and cooling when nobody is around. And yes, it requires a C-wire.

Ecobee Smart Si is a reliable and feature-rich smart thermostat that helps you save as much as the latest model Ecobees in theory. But it can be better; it lacks a touchscreen, which would have made it more convenient to operate, and it does not have some of the convenience features you find on later model Ecobees. It also does not have motion and light sensors. Besides, even if you wanted to buy the six-year-old Smart Si, you might not find it in stores as easily as the Ecobee4.

The Ecobee Smart Si is listed as sold out and discontinued on the Ecobee web site, but you might still be able to find it on Amazon, selling for around $170.


Fast forward five years and the company behind the Smart Si released Ecobee4. Many sources called it the Nest Learning Thermostat killer and chose it over the third-generation Nest as the best smart thermostats available in the market.

The lure of the Ecobee4 is easy to see. The responsive touchscreen display, the remote sensors, smart integrations, and, of course, having your own Amazon Alexa speaker built in.

Ecobee4 still needs a C-wire but if you do not have it, you do not have to call in a professional to rewire your heating and cooling system. You can just use the power extender kit that comes free with your purchase.

Ecobee4 uses room sensors to know if there is somebody in a room and to know that room’s temperature. As such, it can deliver the right amount of heat or cold to every room in your home and only when it is needed.

Ecobee4’s coup de grace is the fact that you can control it by voice, as well as other smart devices that are compatible, with Alexa, even if you do not have Amazon’s own speakers.

Another thing that you would like about Ecobee4 is its wide range of integrations. Ecobee Smart Sirelied on Zigbee to connect with your other smart devices, while Ecobee4 works with Apple Homekit, Samsung SmartThings, Amazon Alexa, and IFTTT recipes.

Comparing Ecobee Smart Si and Ecobee4

To make it easier to compare the Ecobee4 and the Ecobee Smart Si, here is a side-by-side comparison:

  Ecobee4  Smart Si 
Estimated energy savings  23%  23% 
Remote sensors  Yes  No 
Dimensions (inches)  4.29 x 4.29 x 1.03  3.25 x 5.50 x 1.00 
Display size (inches)  3.5  2.5 
Resolution  320 x 480  320 x 240 
Touchscreen  Yes  No 
Thermostat proximity sensor  Yes  No 
Humidity sensor  Yes  Yes 
Temperature sensor  Yes  Yes 
Accessory control  H or D or V  No 
Smart Home/Away  Yes  No 
Follow Me  Yes  No 
Power options  Wired  Wired 
Local weather forecast  Yes  Yes 
Warranty (years)  3  3 
Onscreen alerts & reminders  Yes  Yes 
Free cooling   Yes (with ventilator)  No 
Optimal humidity  Yes  Yes 
Fan dissipation  Yes  Yes 
AC overcool to dehumidify  Yes  Yes 
Mobile apps  Yes  Yes 
Wi-Fi  Yes  Yes 
Home IQ™  Yes  Yes 
Web portal  Yes  Yes 
Programmable fan  Yes  Yes (with c-wire) 
Keypad lock  Yes  Yes 
No annual fees   Yes  Yes 
Desired temperature range  7° to 33°C  7° to 33°C 
Display temperature range  5° to 37°C  5° to 37°C 
Sensitivity  +/- 0.5°C  +/- 0.5°C 
Operating temperature range  0° to 55°C  0° to 55°C 
Display humidity range  20% to 90% RH  20% to 90% RH 
Sensitivity humidity range  +/- 5% RH  +/- 5% RH 
Operating humidity range  5% to 95% RH (non-condensing)  5% to 95% RH (non-condensing) 


One of the biggest and most obvious differences between the Ecobee4 and the Smart Si is how each one looks. The black Ecobee4 has a square form measuring 4.3 inches on all sides. Meanwhile, the Ecobee Smart Si has a rectangular form and is white in color.

The touchscreen display on the Ecobee4 is also bigger with a higher resolution than the Smart Si.

When it comes to sensors, the Smart Si does not have light and motion sensors, which could have helped it get more data to better adjust your programmed temperatures.

The older Smart Si is also cheaper than the Ecobee4, with an $80 price difference.

The biggest difference between the two has something to do with the smarts and the integrations. The Ecobee4 works with most major platforms and IFTTT recipes. If you are looking for a thermostat that can automate your smart home, then the Ecobee4 is for you. Additionally, the Ecobee4 offers more ways for you to interact with it. Like the Smart Si, you can use the Web portal, mobile apps, and the interface on the thermostat itself. But you can also use voice commands, and automate your thermostat using SmartThings, HomeKit, and other platforms.

However, there is very little difference with the thermostats themselves. Both promise up to 23% savings on your cooling and heating costs.

They have the same operating and humidity ranges. They do not require you to pay annual fees, and they both give you access to the energy reports, as well as the heating and cooling features they offer.

If the smart features and integrations are not that important to you, then you would still get the same level of savings as the cheaper Ecobee Smart Si. But if you are the kind of person who likes all the bells and whistles, and the top-of-the-line technological innovations, then you would probably not mind spending more for the Ecobee4.