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Honeywell Home T9 thermostat review: smart sensors, frustrating limitations

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Resideo’s first consumer thermostat with remote sensors doesn’t quite match Ecobee

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In the world of smart thermostats, what separates the top models from the rest of the field is the ability to measure the temperature in more than one spot in your home. That allows you to regulate the heating and cooling functions in the areas where you actually are, instead of where the thermostat is mounted. It’s the next best thing to having multiple zoned HVAC (heating, ventilation, and air conditioning) systems. To do this, smart thermostats utilize small, wireless remote sensors that can detect temperatures and then integrate that data into their algorithms.

Ecobee was the first consumer-based smart thermostat to utilize this kind of feature. Its sensors can both measure temperature and detect presence, so the thermostat’s settings automatically “follow” you around. Nest added remote sensors as an option to its thermostats last year, but the Nest sensors are very limited compared to Ecobee’s; they can only measure temperature and are not able to detect presence at all.

Now. with the Honeywell Home T9, Resideo has a consumer thermostat of its own that supports remote temperature sensors. (Honeywell Home shares a name with the iconic thermostat brand, but it is actually licensed by Resideo, which spun out of Honeywell last year.) The $199 T9 comes with one remote sensor in the box and can support up to 20, compared to the 32 sensors that Ecobee can handle and the maximum of 18 that Nest supports. In addition to measuring temperature and detecting presence in a room, the T9’s sensors also have the ability to measure humidity, which is something Ecobee and Nest can only do from the primary thermostat.

Aside from the remote sensors, the T9 has all of the features you’d expect from a smart thermostat, including support for a variety of HVAC systems, time-based or geofenced scheduling, and a smartphone app to control your system when you’re not home. It also supports both Amazon’s Alexa assistant and Google Assistant for voice control, with support for Apple’s HomeKit platform promised by the end of this year. If you’re looking to integrate it with other smart home products, the T9 works with Samsung’s SmartThings platform and IFTTT, giving it an edge over Nest’s thermostats.

But despite checking all of the feature boxes, using and living with the T9 isn’t quite as nice of an experience as it is with Nest or Ecobee.

Installing the T9 is very similar to installing any other smart thermostat: you match up the wires from your old thermostat to where they need to go on the new one. My simple HVAC system, with just a single-stage oil-based furnace for heating and a single-stage central air conditioning unit, was supported right out of the box. But if you have other, more complex systems, you might need to run extra wiring or spend more time setting up the T9 (or any smart thermostat, for that matter). The Honeywell Home website provides a compatibility checker so you can determine if the T9 will work before you buy.

Where the T9 differs from Nest or Ecobee is its shape: it’s a vertically oriented rectangle that’s narrower than it is tall. That means it did not cover up all of the holes from my old thermostat. So depending on the shape of your current thermostat, there might be some repair work and painting on the wall to do. Resideo says the T9 was designed to hide the holes from old Honeywell thermostats. And unlike the Nest or Ecobee, a backing plate to hide old holes is not included in the box. Resideo sent me a prototype of the backing plate that it will eventually sell to customers to hide the holes, but it was not yet available for purchase at the time of publication.

Aside from that, the T9’s design is modern and attractive, and the large, full-color touchscreen display is bright and easy to read from across the room. Cleverly, it will turn the background of the screen blue when the A/C is on and orange when the heat is running, so you can quickly see what your system is up to at a glance. The touchscreen is also quick and responsive to use.

The T9 comes with one remote sensor in the box, and it has to be mounted on a wall.
Ecobee remote sensor (left), T9 sensor (right). Unlike the Ecobee, the T9 sensor can read both temperature and humidity, and it runs on standard AAA batteries, but it’s much larger.

The T9’s remote sensor (one comes in the box, and additional units can be purchased in pairs for $74.99) is much larger than Ecobee’s and can only be mounted to a wall. There’s no stand included so you can simply place it on a mantle or shelf. The box includes 3M strips to make mounting it easy, but I much prefer the compact size and flexibility of placement that Ecobee’s sensors offer.

On the plus side, the T9’s sensor runs on two standard AAA batteries, which are much easier to replace than the coin cell battery used by Ecobee or the special lithium battery Nest uses. Resideo says they should last a year under typical use.

As mentioned earlier, the T9 sensor can measure humidity in addition to temperature, something neither Nest nor Ecobee’s sensors can do. It can also sense motion and presence, so it can adjust the system to rooms where it detects people actually are. The T9 allows you to select which sensors you want to read from in a given time block, and it will average the system’s temperature based on the multiple readings. The individual sensors are even recognized by Alexa and Google Assistant, so you can use voice commands to set the thermostat based on a specific sensor, which is something that neither Ecobee nor Nest supports.

You can link up to 20 remote sensors to one T9 thermostat and program it based on what they are reading.
The T9 can be programmed based on presence detection or time blocks, but you can’t combine the two.

But beyond that, the T9’s scheduling and people detection options are limited. For starters, the thermostat itself doesn’t actually have a motion sensor in it at all. If you want presence detection in that area, you’ll have to stick a remote sensor next to it. Furthermore, it’s not possible to use the T9’s sensors to trigger home and away status; the only way to do that is by setting up a geofence trigger in the Honeywell Home smartphone app. If you share your home with others and want to change the thermostat’s settings based on whether people are home, you’ll have to install and set up the app on everyone’s phone. That makes it difficult to use geofencing if you have babysitters or other infrequent visitors. Both Ecobee and Nest are able to use their sensors to detect home and away status and adjust themselves without needing to rely on a smartphone-based geofence.

It’s also not possible to mix time-based scheduling with geofencing beyond just a limited night mode for when you’re sleeping. If you are using the time-block schedule to program the thermostat, and your schedule deviates from that program, the system can’t adapt based on whether you’re home without a manual intervention.

Resideo says it designed the system this way based on research and feedback from its customers, who overwhelmingly preferred a simpler setup to a more intelligent one. But this has the effect of making the T9 feel much less smart than its competitors and forces me to manually change its settings far more often than I really should have to with a smart thermostat.

The Honeywell Home app provides extensive control over the T9’s features and settings, but there’s no web-based access for desktop computers.

In addition, the T9 can only be controlled via the thermostat itself, a voice assistant, or the smartphone app. There’s no web-based dashboard to access it with. Owners will get usage reports sent to their email on a monthly basis, but there’s no way to see how the system has been running over a period of time before those arrive.

Overall, the T9 is a good smart thermostat system, with an easy-to-use interface and a decent amount of flexibility in how you can control it. Many of its shortcomings could be addressed with software updates and which could make the T9 a bit more competitive than it is currently. But for now, the Ecobee remains the smart thermostat to beat.

Update, 8:00AM ET, July 23rd, 2019: Clarified the branding between Resideo and Honeywell Home in numerous places. Also added clarification that the T9 is the first Honeywell Home branded thermostat with remote sensors available for purchase at retail, prior to this the brand had thermostats with remote sensors available through professional HVAC installers.

Photography by Dan Seifert / The Verge

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