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Johnson Controls GLAS review: Costly Cortana-powered GLAS thermostat has a striking design, but it's not for everyone

Johnson Controls' $319 GLAS Smart Thermostat has a built-in Cortana speaker and a clear OLED display.

Megan Wollerton Former Senior Writer/Editor
5 min read

Johnson Controls' GLAS Smart Thermostat costs $319. That's 70 bucks more than the Ecobee4 and Nest Learning Thermostat. Given that, the GLAS had better be pretty spectacular to compete. 


Johnson Controls GLAS

The Good

Johnson Controls' GLAS Smart Thermostat has a built-in Cortana speaker and it also works with Alexa and Google Assistant. In addition to its basic capabilities, the GLAS provides indoor and outdoor air quality reports. Its unique, see-through OLED screen surprisingly doesn't get too smudgy-looking after regular use.

The Bad

You're paying a premium ($319) for the OLED touchscreen and the integrated Cortana speaker.

The Bottom Line

The GLAS is a solid smart thermostat, but it isn't a good value if you don't feel strongly about its transparent display and Cortana functionality.

In some respects, it is.

It's immediately clear you're paying extra for the GLAS' neat-looking see-through OLED touchscreen and its built-in Cortana speaker. The Johnson Controls thermostat also monitors the indoor air quality, so you can see, at a glance, if you should circulate your HVAC system's fan. That's a really nice touch. 

The app and the OLED display are responsive and simple to navigate, too, making for a good overall user experience. 

This Cortana smart thermostat also gives air quality reports

See all photos

My issue is with its value. You need to really love the see-through touchscreen and its native support for Microsoft's voice AI to feel good about spending $319 on a single smart thermostat. That said, the GLAS is surprisingly versatile -- it works with Alexa and Google Assistant (assuming you have compatible Amazon and Google devices, since those speakers aren't directly integrated into the GLAS like Cortana is). 

If you specifically want support for Cortana and you really like the GLAS' unique aesthetic, you might not mind its comparatively high price. Everyone else should weigh it alongside some of the other great Wi-Fi thermostats we've reviewed.  

The GLAS is only available in the United States. At the current exchange rate, $319 converts to roughly £250 or AU$440.

Getting to know the GLAS

Installing the GLAS is roughly the same as installing any other smart thermostat we've tested -- with one notable exception. Since it's see-through, you'll have to patch more of the wall behind it. 

Any holes from previous thermostats or weird patches with old paint, will definitely show up when you install the GLAS.

To get around this, Johnson Controls includes a large back plate (which we used), but it somewhat defeats the purpose of having a see-through thermostat to begin with. If you're willing to put in the extra time patching and painting, though, the GLAS will look really neat.

The other thing to note is that the GLAS requires a C-wire. Not sure what that is? You can read more about it here, but definitely consult a professional if you have questions or need help with this (or any) installation. 

If your system doesn't currently have a C-wire, Johnson Controls includes a C-wire adapter in the box with your purchase. Still have questions? Visit Johnson Controls' support page where they discuss all things GLAS installation. 

Here are the basic steps:

  • Turn off power to your current thermostat
  • Remove its faceplate and take a picture of your current wiring
  • Disconnect the wires and unscrew (and remove) the old thermostat's baseplate
  • Route the wires through the GLAS' baseplate (or the back plate first, if using)
  • Screw down the baseplate with the included hardware
  • Connect the wires to the correct terminals
  • Attach the faceplate/wire cover and turn power back on to your thermostat

The GLAS should power on immediately and walk you through the setup. It will ask you questions like, "What time do you usually wake up?" and "What's a comfortable range for when you're at home?" to get a sense of your preferences. The GLAS has internal sensors designed to determine if you're home or away automatically, but giving it an idea of your preferred settings helps it balance comfort and energy savings. 

You can also create a set schedule for your heating and cooling if you typically stick to a routine and would rather not have GLAS decide for you.

Enlarge Image

The GLAS monitors air quality in your home.

Chris Monroe/CNET

Once the GLAS is configured, you can download the GLAS app and create an account, as well as a Microsoft account to use the Cortana speaker. The GLAS app is straightforward, if not a little sparse. But it's easy enough to adjust settings -- or simply check in to see what the current temperature is set to at a glance. Everything you can see on the thermostat itself is also available through the app, including settings schedules, air quality reports and energy usage stats. 


The GLAS app is straightforward and intuitive.

Screenshots by CNET

Using Cortana, Alexa and Google Assistant with the GLAS is easy, too. Let's start with Cortana. Since Microsoft's voice AI is built into the GLAS thermostat, you don't need a separate Cortana speaker. Say, "Hey Cortana, set my temperature to 70 degrees." You can also ask Cortana to change the mode (from heat to cool, or from auto to off, etc.), change the settings from home to away, tell you the current temperature and give you the latest air quality reading. 

Beyond thermostat settings, the Cortana speaker can answer other basic questions about the traffic and weather, as well as set alarms, give you directions and more. The speaker worked well and the GLAS could hear me from 25 feet away at a regular volume when there wasn't other ambient noise in the area. 

Using Alexa and Google Assistant with the GLAS requires separate compatible smart speakers, but it was similarly easy to use with an Amazon Echo Show and a Google Home Max. Ask Alexa or Google Assistant the same things you'd ask Cortana -- to turn up the temperature, to set it to a specific temperature and so on. 

The Ecobee4 has a built-in Alexa speaker, but also works with Cortana and Google Assistant. While the Nest Learning Thermostat doesn't have any built-in voice speakers, it works with Alexa, Cortana and Google Assistant commands (when you have a separate Amazon, Cortana or Google speaker). Alexa and Google Assistant both offer a wide variety of integrations with third parties, whereas Siri, Cortana and Samsung's assistant, Bixby, are still behind. 

Cortana certainly has more work to do in terms of adding partners (today it works with Ecobee, Insteon, Nest, Philips Hue, SmartThings and Wink), but this integration with Johnson Controls is a positive step forward. Cortana was very responsive when I asked questions about the thermostat -- as well as about other general things like, "What's the weather today?" and "What time is it in Seoul, South Korea?" Microsoft's voice AI even told me a joke when I asked for one. 

In this way, Cortana is fairly conversational, but it had a more robotic-sounding edge to its voice that made its natural language skills sound a little behind Alexa, Google Assistant, and even Siri. Alexa now has its own Cortana skill, too, so folks with Alexa speakers and a Microsoft account can ask things like, "Alexa, open Cortana" -- "What new emails do I have?" and "What's on my calendar for tomorrow?" 

This new Alexa skill provides a nice bridge for anyone using Outlook and other Microsoft applications, but who prefer Alexa's functionality as a voice assistant. 

Find out more about what Cortana can do here.

The verdict

The GLAS is the first smart thermostat we've tested with an integrated Cortana speaker. At $319, it's very expensive, but it also has some things other high-end DIY models like the Ecobee4 and the Nest Learning Thermostat don't have -- Cortana, a see-though design, air quality readings. 

If those things are priorities for you, the $319 might be worth it. But many people won't want to pay a premium for native Cortana support and a transparent OLED screen, however distinctive its looks. 


Johnson Controls GLAS

Score Breakdown

Features 8Usability 7Design 7Performance 7