Sensi Thermostat: ST55 vs UP500W- Do you live in an Apple Smart Home?

Sensi thermostats are Emerson’s range of smart thermostats.

There are only three models in the range- ST55, UP500W and the ST75, although at first there might seem more.

One of the reasons, is that each Sensi thermostat has a Pro version or a DIY version.

Pro versions of these Emerson thermostats come with a 5 year warranty as long as they are installed by an HVAC professional.

The DIY thermostat comes with a 3 year warranty regardless of who installs it.

This article will focus on the ST55 and the UP500W models because they are almost identical.

I have reviewed the UP500W before- in a comparison with the Nest thermostat.

There is only one difference between the Sensi ST55 and the Sensi UP500W thermostats.

The ST55 is compatible with Apple HomeKit and the UP500W isn’t.

And that’s it- well almost.

The HomeKit compatible thermostat must be powered by a “c” wire whereas the UP500W can be powered by batteries.

Apart from that these two Sensi wi-fi thermostats are exactly the same.

In fact, looking at the two thermostats, the only way to tell the difference between them is that the ST55 has the “Sensi” logo at the top whereas the UP500W has the “Emerson” logo.

Take a look at my comparison chart of the main features to find out just how alike these two smart thermostats are.

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These two thermostats are not the modern pieces of art that the Nest or the Ecobee thermostats are but they lack in their looks, they more than make up for in their reliability.

Size- wise, these two Sensi thermostats are much wider than the Nest or the Ecobee but they are about the same depth and height.

Also, the Sensi thermostats do not have color screens or touch screens.

The back lit screen although it looks a little dated, it offers a very clear display with lots of information. The blue light does not stay on all the time and one of the buttons needs to be pressed on the front of the thermostat to activate it.

As well as displaying basic information such as the time, status of the Wi-fi connection and the battery level (if appropriate) there is lots of other useful information to feast your eyes on.

This includes; the current temperature in the room, the set point, whether the system is heating, cooling or off, whether the fan is on auto or off and whether the schedule is on or off.

All of these features can be changed by either using the buttons on the right hand side or those along the bottom.


HVAC Compatibility

The ST55 and the UP500W both work with almost all 24V HVAC systems.

They will work with gas, oil, electric or dual fuel systems.

They will not work with electric baseboard heating systems or millivolt systems.

On a conventional system, these smart thermostats will work with 2 stages of heat and 2 stages of cooling but on a system powered by a heat pump it works with 4 stages of heating and two stages of cooling.

Both of these wi-fi thermostats will work with HVAC accessories such as humidifiers and dehumidifiers.


The ST55 and UP500W need to have schedules set up manual.

Unlike the Nest, which learns your preferences over time, you need to “tell” your Sensi thermostats what temperatures you like and when.

Schedules can be set up for each day or days can be grouped together so that they have the same schedules.

Each schedule can have up to 7 settings- a setting is a time and a temperature set point.

Fortunately scheduling is very easy to do via the app.

Here is a video that shows you just how easy it is.

The video is very easy to follow, as long as you have your Sensi app open at the same time!

Or if you want a written step by step guide, go here.

Screen details

These details were discussed earlier.

Room sensors

Neither the ST55 or the UP500W work with remote sensors.

These are an advanced feature, most widely used with Ecobee thermostats.

They are small plastic buttons that sit in different rooms in your home and connect wirelessly to your thermostat.

They send back information about the temperature in the room or whether the room is occupied.

This helps smart thermostats to run more efficiently because it knows which rooms are unoccupied and what the average temperature is across the whole house.


But they do have geofencing capabilities.

Geofencing uses a smartphone’s location to turn a smart device (such as a Sensi thermostat) on or off when you are away from home.

It is very useful if you forget to turn you thermostat manually before you leave your house and it is wonderful if you are returning home on a cold night because the thermostat will start to heat your home before you get home.

Energy reporting

Unfortunately, neither of these two Sensi thermostats have energy reporting.

This is the ability of a thermostat to track how you use your energy on an hour by hour day by day or week by week basis.

These reports can help because they provide data that over time highlights when your thermostat is running most effectively.

Remote Access

This is the ability to control your thermostat if you are the other side of the room or the other side of the State.

Both of these thermostats use the same app to control them.

The app is available for iPhones or iPads and Android phones and tablets.

In order for the app to work on your Apple devices, you will need iOS 10 or later.

Your Android devices need to be running version 4.2 or higher.

As well as being able to control your Sensi thermostat via an app you can also control it from a traditional web browser.

This is fantastic news for all of us who still spend lots of time working on laptops.

Home Automation

So this is where thermostats differ because the ST55 is HomeKit compatible and the UP500W isn’t.

But, both thermostats work with Amazon Alexa and Wink hubs.

How to set up your Sensi thermostat to work with Alexa

Before you can pair your thermostat with your Echo device, make sure that you have the Sensi app and the Alexa apps set up on your phone.

Read the step by step instructions on this page ( to pair your devices.

It should only take a couple of minutes to do.

Once completed, you can ask Alexa to;

Raise the temperature
Lower the temperature
Set the temperature
Set the house to cool
Set the house to heat
Set the house to auto

Or you can ask Alexa what the current temperature is.

How to set up your thermostat to work with Wink

In many ways this is very similar to the process described above.

You need to have the Sensi and the Wink apps downloaded and set up on your phone.

In your Wink app, just tap on add a product, then tap on heating and cooling and then select Sensi thermostat.

The app will quickly walk you through the remaining steps.

Working with HomeKit

There is a step by step guide to help you configure your ST55 to work with HomeKit.


Both of these Emerson thermostats connect directly to your home’s wi-fi as long as it is 2.4 Ghz. They don’t need to connect via a smart hub instead.


This is the only other difference between the ST55 and the UP500W thermostats.

The HomeKit enabled thermostat can only be powered via a “c” wire, whereas the UP500W can be powered via a “c” wire or two AA batteries.


These thermostats come with a whooping 3 year warranty.

Pros and Cons

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