If you have electric baseboard heating and you’re shopping for a smart thermostat, one of the first questions you’ll hit is voltage: is your heater 120V or 240V? The answer determines which thermostat works, and getting it wrong means buying the wrong device.

This guide covers how to check, and what it means for your purchase.

Line Voltage vs Low Voltage: The Basics First

Before getting into 120V vs 240V, it helps to understand that baseboard heaters use a different type of thermostat than a gas furnace or central AC.

Low-voltage systems (furnaces, heat pumps): The thermostat is a signal switch running on 24V. Nest, ecobee, and Honeywell are low-voltage thermostats. These don’t work with baseboard heating.

Line-voltage systems (electric baseboard heaters): The thermostat carries the full household current (120V or 240V) to the heating element. The thermostat IS the switch. Purpose-built line-voltage thermostats like Mysa and Sinopé handle this.

If you have baseboard heaters, you need a line-voltage thermostat. The 120V vs 240V question is about which version of line-voltage you have.

How to Tell If Your Baseboard Is 120V or 240V

You have three reliable methods:

Method 1: Check the Circuit Breaker

Go to your electrical panel and find the breaker that controls the baseboard heater in question.

  • Single breaker (one switch): Likely 120V, single-pole circuit
  • Double breaker (two switches tied together): Likely 240V, double-pole circuit

This is the fastest check. It’s not 100% definitive (some older panels are wired oddly), but it’s right for the vast majority of Canadian homes.

Method 2: Check the Heater’s Label

Most baseboard heaters have a label on the unit itself (often inside a small access panel or on the back). Look for the voltage rating:

  • “120V” or “120V AC” = 120V heater
  • “240V” or “208-240V” = 240V heater
  • Some labels show watts and amps: at 120V, a 1,500W heater draws 12.5A; at 240V, a 1,500W heater draws 6.25A

Method 3: Count the Wires at the Thermostat

Pull the faceplate off your existing baseboard thermostat and count the wires in the box:

  • Two wires (one black, one white): Almost always 120V, single-pole circuit
  • Two black wires (or two red wires): Likely 240V, both are hot conductors
  • Four wires (two black, two white, or two black, two red): Likely 240V with a neutral, or a double-pole 120V setup

If you see two wires and they’re the same colour (both black or both red), that’s a strong indicator of 240V. If one is black and one is white, it’s most likely 120V.

When in doubt: call an electrician. Baseboard wiring carries full household current. Misidentifying the voltage and buying the wrong device is a safety issue, not just a nuisance. In most Canadian provinces, homeowners need a permit or a licensed electrician for line-voltage thermostat installation.

Single-Pole vs Double-Pole Thermostats

This distinction comes up when shopping:

Single-pole thermostat: Controls one wire (the hot conductor). Turns the heater from full power to minimum, but doesn’t cut power entirely. The heater never fully de-energizes. Designed for 120V circuits.

Double-pole thermostat: Controls both hot conductors. Cuts full power to the heater, so it turns off entirely. Required for 240V circuits and code-compliant in many jurisdictions. Some homeowners prefer double-pole even on 120V for peace of mind.

For smart thermostats, this distinction matters:

  • Mysa V2 handles both 120V and 240V (double-pole). It cuts full power in all configurations.
  • Sinopé models are available in both single-pole (120V) and double-pole (240V) configurations, so check the specific model when ordering.

Which Smart Thermostats Handle Each Voltage

Thermostat 120V 240V Max Wattage Notes
Mysa V2 Yes Yes 3,600W @ 120V / 3,800W @ 240V Double-pole; one model handles both
Sinopé TH1300ZB / TH1300WF Yes No 3,600W @ 120V Single-pole 120V model
Sinopé TH1500ZB / TH1500WF No Yes 3,840W @ 240V Double-pole 240V model

Full spec comparison of line-voltage smart thermostat models with voltage range and wattage limits

Mysa V2 has a meaningful practical advantage here: one model handles both 120V and 240V. You can buy the same thermostat regardless of your voltage, and it self-configures during setup (the app asks for your voltage during the wiring step).

Sinopé has separate models for 120V and 240V, so make sure you’re ordering the right one. The model numbers help: TH1300 = 120V, TH1500 = 240V.

Safety: When to Call a Pro

Line-voltage work is not the same as replacing a doorknob. The wires in your baseboard thermostat box carry the same voltage as your kitchen outlets, and they can injure or kill if handled incorrectly.

Call a licensed electrician if:
– You’re not confident identifying your wiring
– You find wiring that doesn’t match the patterns described above
– Your home has aluminum wiring (common in homes built in the late 1960s and 1970s)
– The thermostat box shows signs of burning, melting, or overheating
– Your province or municipality requires a permit for thermostat replacement (check local electrical code)

DIY is reasonable if:
– You’ve correctly identified your voltage
– The wiring in the box is in good condition
– You’ve turned off the circuit breaker and verified power is off with a voltage tester before touching anything
– Your province allows homeowner thermostat replacement with or without a permit

When in doubt, see Smart Thermostat Installation: DIY vs Hiring a Pro for a cost comparison on hiring a local electrician.

Wattage: Don’t Overlook This

The voltage question gets most of the attention, but wattage matters equally. Your thermostat has to handle the total load of every heater it controls.

If you have two 2,000W baseboard heaters on one thermostat circuit, the thermostat needs to handle 4,000W continuously. Most smart baseboard thermostats top out around 3,600–3,840W, below that combined load.

In practice, most individual room zones in Canadian homes fall within the thermostat’s rated capacity. But if you’re wiring a large open-plan space with multiple heaters on one circuit, add up the wattages before buying.

Bottom Line

You have… Buy this…
120V baseboard heater Mysa V2 or Sinopé TH1300 (120V model)
240V baseboard heater Mysa V2 or Sinopé TH1500 (240V model)
Not sure Mysa V2 (works with both)
Central gas furnace or heat pump Nest, ecobee, or Honeywell, not Mysa or Sinopé

For the full guide to baseboard-compatible smart thermostats, see Best Smart Thermostats for Electric Baseboard Heating in Canada.

Frequently Asked Questions

Can I use a 240V thermostat on a 120V heater?
No. A 240V thermostat wired to a 120V circuit won’t function correctly and could be a safety hazard. Use the correct voltage rating for your circuit.

Does Mysa V2 work with both 120V and 240V?
Yes. One Mysa V2 handles both voltages. The setup app asks for your voltage and configures accordingly. This is one of Mysa’s practical advantages over Sinopé, which has separate models for each voltage.

Can I replace my baseboard thermostat myself in Ontario / BC / Alberta?
Canadian electrical code allows homeowners to do their own electrical work on their own homes in most provinces, but a permit is often required, and the work must comply with code. In practice, many homeowners replace baseboard thermostats without a permit, but this varies by municipality and is worth checking. For line-voltage work, getting it inspected is good practice even if not required.

What’s the maximum wattage the Mysa V2 can handle?
3,600W at 120V and 3,800W at 240V. If your heater(s) on a single thermostat circuit exceed this, you’ll need to check alternative options or split the load across multiple thermostats.

Why does my old thermostat show “120/240V”? What does that mean?
Some older mechanical thermostats were rated for both voltages and could be used on either circuit depending on how they were wired. Smart thermostats generally can’t do this with the same flexibility. Check the specific smart thermostat’s rated voltage before buying.