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Are Smart Thermostats Universal? 3 Things You Need To Know

Are Smart Thermostats Universal

A smart thermostat boasts the ability to learn your home’s unique heating and cooling patterns to help you save on energy costs.

It also allows you to control your HVAC system remotely and takes the hassle out of scheduling your usage.

But while they are easy to install, are smart thermostats universal?

Smart thermostats are not universal and cannot be installed right out of the box into any type of HVAC system. When buying a smart thermostat, you need to first verify that it is compatible with your existing heating and cooling system, concerning the voltage and wiring, in particular.

In this article, I will talk about the things you need to know before buying a smart thermostat and installing it.

3 Things You Need To Know About Smart Thermostats

Smart thermostats are not universal and are not one-size-fits-all devices. 

Below are a few things that you need to look into before you buy and install one into your existing heating and cooling system. 

Most Smart Thermostats Only Work With Low-Voltage Systems

Most smart thermostats are only compatible with low-voltage 24-volt HVAC systems. These include smart thermostats from the most common brands like Ecobee, Honeywell, and Nest. 

A low-voltage HVAC is also called central HVAC, central heat, or central air system.

One way to know you have central heat or central air is when you have a single thermostat at home that controls a large furnace located in your garage or basement, perhaps along with a heat pump. 

In this case, your system would be compatible with almost any kind of smart thermostat.

If you have a line voltage system for your HVAC, then it won’t be compatible with the most popular smart thermostats available nowadays. One example of a line voltage system is when you have a separate pair of heater and thermostat in every room in your house. 

Installing a smart thermostat into a complex HVAC system with multiple components such as heat pumps, dehumidifiers, and ventilation units might require a professional HVAC technician to do the job.

This helps ensure that no damage is done to your system.

Most Smart Thermostats Need a C-Wire

Most Smart Thermostats Need A C Wire

A smart thermostat is easy to install yourself if you know your way around wires.

And one thing you need to check first is whether you have enough of them.

For one, you will likely need a common wire or a C-Wire to plug into the C-terminal and to provide your smart thermostat with continuous power.

More specifically, a C-Wire will generate 24 volts of electricity, which will provide the amount of power required to maintain the WiFi connection and support the device’s special features like a lighted touch screen.

However, if your smart thermostat uses batteries, you won’t need a C-Wire. There are also WiFi thermostats that are dual-powered and can work with either C-Wire or batteries. 

Not All Smart Thermostats Support All Smart Devices

Smart thermostats are also not universal when it comes to their ability to support or connect with other smart home devices, like smart lights, cameras, smoke alarms, and locks.

Not all of them can work with the same set of smart home technologies. 

So it would help if you got a thermostat that is compatible with the other devices you already have or the ones you plan on getting for your smart home in the future. 

For example, if you have the Nest outdoor and indoor cameras and the Protect smoke alarm, you might want to get the Nest Learning thermostat. But you don’t need to stick with similar brands or manufacturers because a lot of smart thermostat models support third-party devices, too.

What’s important is you make a list and see which one ticks the most number of boxes.

You may also want to look at a smart thermostat’s IFTTT (If This Then That) support. This is a feature that allows you to create recipes with several other IFTTT-enabled devices.

For example, you can create a recipe that triggers your thermostat and turns on your air conditioner once you come home and your smart lights turn on.

Another feature you may want is support for smart speakers and virtual assistants like Amazon Alexa and Google Assistant.

This way, you can control your smart thermostat by just issuing voice commands. You don’t even need to get your phone and open your thermostat’s mobile app anymore. 

Smart Thermostats for High-Voltage HVAC Systems

There are, however, a few smart thermostats that work with high-voltage heaters.

These thermostats are specifically designed for radiant, baseboard, fan-forced convection heater types instead of the more common central heat systems. 

One example of this type of thermostat is the Mysa Smart Thermostat on, which is known for its elegant industrial design. Mysa supports a bunch of other smart home devices, including Google Assistant, Apple HomeKit, and Amazon Alexa.

Learn more: Can smart thermostats be used with any boiler?

How To Check if Your Existing Thermostat Uses a C-Wire

If you live in an old home with an old heating system, there’s a good chance you won’t see a C-Wire. This is because old thermostats do not require one.

But to know for sure whether your current thermostat has a C-Wire, follow these steps:

  1. Turn off the power. Make sure to turn off your thermostat as well as the switch or breaker box controlling your heating equipment or your furnace. 
  2. Make sure your system is off. Change the temperature on your thermostat. If you don’t hear your HVAC system turning on within 5 minutes, you can be assured that the power is off. However, you can skip this step if you have a digital thermostat and the display has turned blank.
  3. Take out your current thermostat from its wall plate. Remove your current thermostat gently. Depending on how it was attached, you may need to use a screwdriver or simply loosen some clasps or buttons. When you do this, do not detach any of the wires.
  4. Check if there is a C-terminal. Check the wiring at the existing wall plate and look for the C-terminal. This is simply a wire slot with a letter “C” label on it. If there is a C-terminal with a wire connected to it, then it means your current thermostat is using a C-Wire. If there is no C-terminal, then it isn’t.

Check out: Do Smart Thermostats Work With Heat Pumps? 9 Facts Revealed

What To Do if Your Thermostat Doesn’t Have a C-Wire

If your current thermostat doesn’t have a C-terminal and therefore doesn’t have a C-Wire, you can use a C-Wire adapter to make the necessary connection. 

Keep in mind, some homes may have a C-wire that is not used and might be hidden in the wall. Be sure to check out this possibility, as it can save you the time and money spent obtaining an adapter.

To learn more about dealing with C-Wires for your thermostat, check out this page.

The best option, however, is to call a professional technician to deal with the wirings and replace your existing thermostat with a smart one.


Smart thermostats are not created equal and are, therefore, not universal devices.

Unfortunately, this means that you cannot take out your existing non-smart thermostat and just replace it with any smart thermostat you find at the store. 

Avoid purchasing a smart thermostat just because the manufacturers tell you it is easy to install by yourself.

Instead, you should consider its compatibility with your HVAC system, your wiring, and your other smart home devices before making a commitment to any brand or product.

Read next: Can a Smart Thermostat Detect Room Occupancy? The Truth