Low Voltage vs High Voltage: 4 Ways to Tell the Difference


Wondering about the difference between low voltage vs high voltage thermostats? Whether you need a thermostat replacement or are just looking to make a smart upgrade, thermostat voltage is important to know. The thermostat you choose will depend heavily on what’s compatible with your home. 

To find a thermostat that works for you, you’ll first have to know the voltage of your current thermostat. Low voltage thermostat wiring is very different from high voltage thermostat wiring. Also, your thermostat has to be able to handle the amount of voltage running from your heating or cooling source. 

So, we’re here to help with four ways to tell the difference between low voltage vs high voltage and some smart thermostat options for each. But first, let’s learn a little more about the different types of voltage. 

Types of Thermostat Voltage 

Luckily, there are only two main types of thermostats — low voltage and high voltage. So, there aren’t too many options to consider when determining which system you already have. All traditional thermostats will fall into one of these two categories. 

Technically, the terms “low” and “high” voltage are relative, and the definition varies by context. What is considered low and high voltage can also vary between applications and local laws and regulations. 

However, generally speaking when comparing low voltage vs high voltage, a low voltage range is usually up to the 50 volt mark. Anything higher than that is considered high voltage. 

What is Low Voltage? 

What is considered low voltage? Typically, low voltage means your thermostat can handle between 12 volts and 24 volts of electricity. 

Low voltage thermostats don’t power individual heaters, instead they control a home’s main HVAC source and indirectly heat your home through control signals. A low voltage thermostat sends a signal to turn your HVAC system on or off, and the HVAC system then burns fuel (gas, oil, etc.) to heat your home.

Most homes throughout North America have low voltage thermostats. They’re used to control a variety of HVAC systems, including boilers, furnaces, and ducted heat pumps. 

What is High Voltage? 

What is considered high voltage? To compare low voltage vs high voltage capacity, high voltage thermostats range from handling 120 volts to 240 volts of electricity. 

A high voltage (or to use the technically correct term “line voltage”) thermostat is the opposite of a low voltage system. There’s a direct connection between your home’s main electricity circuit, your high voltage thermostats, and your heaters. To control room temperature, your line voltage thermostat controls how long your heaters stay turned on. A heating element in your heater then converts electricity into space heating. 

High voltage thermostats are more commonly used with radiant, convection, or resistance heat sources. Examples of these include baseboard or wall heaters, fan-forced heaters, and in-ceiling radiant heat. 

What is Line Voltage? 

In terms of residential home heating, line voltage and high voltage are interchangeable terms. So, both refer to the same thing (ie. line voltage thermostat wiring is the same as high voltage thermostat wiring). 

So, What is the Difference Between Low Voltage and High Voltage? 

To put things simply, a low voltage thermostat is only used to deliver a signal to a heating system that tells it what to do. This only requires a very small amount of electricity, so that’s why they’re known as low voltage.  

In contrast, high voltage thermostats regulate how long heating systems are left on and there’s a direct connection of electricity between the thermostat and the heater. A heating element inside the heaters is what converts the 120V – 240V of electricity into space heating. 

Low Voltage vs High Voltage: How to Tell the Difference

If you’re hoping to upgrade to a smart thermostat that can help save, the first step is to determine what voltage your thermostat uses. Knowing if you have a low or a high voltage thermostat will help you find a compatible thermostat replacement. 

So, here are 4 ways to tell if you have a low voltage or line voltage thermostat.  

1. How You Heat or Cool Your Home

There are many different home HVAC systems, which unfortunately means that there’s no one-size-fits-all solution for smart home thermostats. 

To tell the difference between low voltage vs high voltage thermostats, a good starting point is to consider your HVAC system (i.e. how you heat and cool your home). This makes a huge difference when choosing a new thermostat.

Generally, there are two types of HVAC systems: 

  • Central HVAC systems controlled by low voltage thermostats.

  • And electric HVAC systems controlled by high voltage thermostats or other means. (For example, ductless mini split heat pumps are controlled by IR technology instead of a traditional thermostat).  

Central HVAC Systems

Central HVAC systems usually have one central heating or cooling source controlled by a single thermostat that provides heat or AC to different distribution systems in a home. Central HVACs are ducted systems, or possibly hydronic (radiator) based, that can use a variety of heating fuels such as water, gas, oil, wood, etc. 

Furnace heating, forced air, ducted heat pumps, and boilers are all different types of central HVAC systems. 

If you only have 1-2 thermostats in your home that control a central HVAC system, it’s likely that you have a low voltage thermostat. 

Electric HVAC Systems

Homes with electric HVAC systems usually have multiple thermostats, as many as one per room. Electric HVAC systems are powered entirely by electricity. 

Baseboard heaters, fan-forced heaters, in-ceiling radiant heat, and electric in-floor heating are all examples of high voltage electric HVAC systems. 

Ductless mini split heat pumps are also electric systems, but are controlled by IR signals. So, instead of a traditional thermostat wired into a wall, mini splits are controlled by a handheld remote or a smart mini split thermostat.  

If you have multiple thermostats throughout your home controlling your electric HVAC systems, you likely have high voltage thermostats. 

2. Check Your Thermostat Voltage

An easy way to confirm if you have a low voltage vs high voltage thermostat is checking your thermostat voltage. To do this, you have a couple of options. 

First, you could check the labeling under the cover of your thermostat. If you have a high voltage thermostat, most jurisdictions require it to be labeled with clear “HIGH VOLTAGE” or similar warnings or with the voltage itself (e.g., “240V”). Most, but not all, low voltage thermostats should also show their voltage rating clearly labeled on the exterior of the case. 

Second, you could try using a voltage meter to measure how much voltage is going to your thermostat. The accuracy of this measurement will depend on the voltage meter being used. But, given the huge difference between low and high-voltage thermostats, it makes interpreting the measurement easier. Note: Make sure to take necessary safety precautions before trying this method. 

3. Number of Thermostat Wires

Another way to figure out whether you have a low voltage vs high voltage thermostat is to look at the number of wires going into it.

Safety first: Before inspecting your thermostat’s wiring, be sure to turn off power to your thermostat from the circuit breaker. This is especially important if you must first remove your thermostat’s plastic cover to access the wiring for inspection.

What is Low Voltage Wiring? 

If you can see lots of small, multi-colored wires, you have a low voltage thermostat. Another way to tell is by looking at the wires to see where they go. Most low voltage installations push the wires through a small hole into drywall, whereas high voltage installations will run wires to a nearby electrical box. 

To illustrate, here’s an example that shows low voltage thermostat wiring:

low voltage thermostat wiring

What is Line Voltage Wiring? 

If you instead see a smaller number of wires that are separated into colored groups (e.g., black and red or black and white), you have a line/high voltage thermostat. Here’s an example of high voltage thermostat wiring: 

high voltage thermostat wiring

4. Thickness of Thermostat Wires 

When comparing low voltage vs high voltage, you can also look at the thickness of your thermostat’s wiring. If your thermostat has large, thick wiring, it is high voltage. The smaller and thinner wires found in low voltage thermostats cannot carry high voltages.

Finding the Right Smart Thermostat

Historically, there weren’t many options when it came to the type of thermostat your home used. Thanks to advances in technology and the growing adoption of smart home ecosystems, this is no longer the case. 

When shopping for a smart thermostat, there are a few things to consider in addition to your HVAC system and whether you have a low voltage vs high voltage thermostat: 

  • Confirm compatibility, which isn’t just about knowing if you need a low or line voltage smart thermostat. Other considerations include max wattage, connectivity, and the number of wires needed for any smart thermostat you’re considering. Most smart thermostats have compatibility information or an interactive quiz on their website, so be sure to check that out before purchasing.

  • Consider smart features included in each smart thermostat’s app. The number of features and how features work differ between brands. So, it’s important to review this information to ensure you’re getting the best thermostat for you. For example, if seeing how much energy you’re using and saving is important to you, you’ll want to find a smart thermostat with Energy Charting

  • Learn about smart home integrations to make sure that the smart thermostat you choose is compatible with your favourite smart home assistant. For example, if you have Google Home smart speakers throughout your home, you’ll want a smart thermostat that’s compatible with Google Home. The same could be said for Alexa and Apple HomeKit

  • Compare competition on basics like pricing and return policy. If you really want to protect your investment, look for a smart thermostat with an Energy Saving Guarantee. Also, be sure to read customer reviews!

  • Look for extras that will make your daily life even easier. For example, homes with electric heating can have multiple different HVAC systems. So, Mysa makes products for electric baseboard heaters, in-floor heating, and mini split heat pumps that can all be controlled in the same app.  

Now that you know if you have low voltage vs high voltage thermostats, to help you find the best smart thermostat for you, we have some suggestions. 

Low Voltage Smart Thermostats

If you have a low voltage thermostat, smart thermostat options to consider include: Google Nest, ecobee, and Hive. All three brands have products that would be compatible with most low voltage thermostats and central HVAC systems. 

High or Line Voltage Smart Thermostats 

If you’re looking for a high voltage smart thermostat, Mysa Smart Thermostats are an option. Our line of products include smart thermostats for electric baseboard heaters, in-floor heating, mini split heat pumps, and window and portable air conditioners. However, if your baseboard heaters are a two-wire only system (i.e. there are only two wires total in your gang box), check out Sinope

Mysa is compatible with all major smart home assistants and our app has a ton of energy-saving features. If you’re curious to see what Mysa products could work for your home, check out our thermostat quiz

Another consideration if you’re upgrading to smart line voltage programmable thermostats is to make sure you have multi zone smart thermostat control for extra savings. 

Low Voltage vs. High Voltage Made Simple 

If you’re hoping to upgrade to a smart thermostat, it’s important to understand the difference between low voltage vs high voltage. While low voltage thermostats are popular throughout most of North America, electric heating is common in certain regions. Plus, it is possible to have multiple HVAC systems, which could mean thermostats throughout your home with different voltages.  

Here’s a quick summary of how to tell the difference between line voltage vs low voltage: 

Low VoltageHigh/Line VoltageUsually operates in the 12V - 24V rangeUsually operates in the 120V - 240V rangeHas several multi-coloured wiresHas fewer grouped red/black/white wiresHas thinner wires due to low voltageHas thicker wires due to high voltageUsed for central HVACs (e.g., furnace, boiler, etc.)Used for electric HVACs (e.g., baseboard heaters)Often labeled with high voltage warnings

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by LastSale
by LastSale