Low Voltage or High Voltage Heating – What’s the difference?
Brad Pretty, 3 years ago   |    12   |    3 min read   |    46815

How you heat your home makes a big difference when you’re shopping for smart thermostats. Home heating systems can vary a lot, and there’s no one-size-fits-all solution for smart home heating thermostats. Smart thermostats offer a lot of benefits: they can help you save money, or let you put the finishing touches on your smart home. The first thing that you can do is to determine whether you have a Low Voltage heating system or a Line Voltage (also known as High Voltage) heating system.

It comes down to a very simple question: How do you heat your home?

In North America, the majority of people rely on furnaces to do just that. Whether it’s natural gas, oil, propane, or wood, most houses get their heat from different distribution systems running directly from a central furnace. It might be a duct-based system, or it may be hydronic (radiator) based heating. If you use one of these systems, you most likely regulate your home heating with Low Voltage thermostats.

The electricity use for these types of thermostats is much less demanding than Line Voltage, as described below. The current going through is not actually being converted to heat – it uses another fuel source. They typically run at 24V and control blowers, fans, and pumps but do not power them. If your house has ducts and has one central thermostat for both air conditioning and heating, it’s almost sure that you have a Low Voltage system.

Still not sure? Well, let’s look at the wires!

If you see a setup similar to this with numerous, small, thin, multi-coloured wires going into a board, you have a Low Voltage thermostat. There are many different options for low voltage smart thermostats, many of them brands you may have heard of. We’ve already done the research for you here.

Although most North American homes use Low-Voltage systems, there’s a mix of both older and newer homes that use Line Voltage heating. Millions of them, in fact! This is commonly referred to as “electric heating” and if you have baseboard or forced-fan heaters as your main source of heat, you’ll need a Line Voltage compatible thermostat. You’ll usually need one for every heater, or at least one per room. These thermostats actually convert the house’s incoming current (120V or 240V) into usable heat. Each thermostat also has a limit of how much current they can handle, which we detail here.

The wires will usually look like this:

Or something very similar. There will be between 2-4 thick wires separated into either black and red or black and white groups.

For a long time, there weren’t a whole lot of options for your smarthome setup if you relied on Line Voltage thermostats for your home heating. Luckily, there’s now the Mysa Smart Thermostat – a device that comes fully featured with the same smarthome integrations, heater zoning, and app support that people have experienced with Low Voltage smart thermostats for years.

The physical differences between Low Voltage and High Voltage thermostats take place mostly under the hood. High Voltage thermostats are usually bigger in size – it has to contain a heat sink because of the active current passing through it.  However, this current ensures that the electronics remain powered without the need for a battery. Low Voltage thermostats, in comparison, often use a process called power-stealing, which allows the device to run on a small battery and recharge by sapping small amounts of power from the main line.

About a third of Canadian households and 10% of American households run on Line Voltage heating systems. While they aren’t the most common way to heat a house, a lot of people rely on electricity for their comfort. With so many options for people with Low Voltage systems to take the next step, it only makes sense that High Voltage customers aren’t left in the cold.

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  1. Marilyn MacKay-Lyons

    We currently have an Axicom thermostat (installed in 2006) to regulate in-floor heating of our living room. Can you tell me if it’s a low-voltage thermostat?

    1. Brad Pretty

      That’s a hard question. While in-floor heating is by nature a high voltage setup, there are a variety of different configurations for the thermostats including using a relay so that the actual controller is only 24V instead of 120V or 240V. Your best bet is to google the model number and see if there’s any information on the voltage it uses.

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  4. jimb

    i have a mix of low and line voltage thermostats in my plant. Could smart thermostats for them both be run on the same app?

    1. Brad Pretty

      You can use an intermediary platform like SmartThings, Apple HomeKit, or Google Home to control them all at once.

  5. jimb

    you don’t have a dedicated app? Or to do what I want you’d have to use one of those suggested? Can you email and I’ll send you my work number to discuss.

  6. Bret

    What would happen if the power went out? Do the thermostats reset automatically? I’m interest in installing these in a vacation home that is on an off-peak power system. The utility company will shut off power during peak periods, so, the thermostats would need to reset when the power comes back.

    1. Jacqueline Clarke

      Hi Bret!

      In the event of a power outage, all or your settings and schedules will be saved to our cloud-based server, all of your preferences will begin automatically once the power returns. If you only lost power, then Mysa will automatically reconnect to the internet and reset its internal clock. In this case, all of your settings will resume when the power returns. If you lose both internet and power, then Mysa will continue trying to re-establish a connection. Until a connection is found.

      For more information, please visit: https://help.getmysa.com/hc/en-us/articles/360030713031-What-if-theres-a-power-outage-or-the-internet-goes-down-

  7. Callum Palmer

    I did not realize that there were so many differences between low and high voltage heaters. It is especially interesting to see how the wires will look for this kind of configuration. Although, I would assume that you’d want a professional electrician to set it up just to make sure it is done correctly.

  8. Gabe

    Do you intend to begin offering low-voltage thermostats one day so we can control our low-voltage furnace thermostat with the same app and settings as we do with our in floor and baseboards?

    1. Alexander Chafe

      Hey, Gabe. We have no immediate plans to expand our product line to include thermostats for low voltage heating systems. However, who knows what the future will bring! At this time though, we would suggest Nest or Ecobee to control low voltage heating.

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