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Electric baseboards need a different kind of smart thermostat
Updated
A furnace thermostat switches a 24 volt signal. A baseboard thermostat switches the full 120 or 240 volts that feed the heater. They are not interchangeable. Of the seven picks here, only the Mysa Smart Thermostat V2 for Baseboards is made for line voltage.
This is line voltage work. Google says high voltage thermostats should only be installed or removed by a professional. Turn the breaker off, and hire a licensed electrician unless you are qualified.
How to tell you have line voltage
- Google: the thermostat is often labeled 110, 115, 120 or 240 VAC and has 2 to 4 thick wires, often joined with wire nuts.
- ecobee: look for L1 and L2 labels on the connectors.
- Mysa, from the other side: thin wires labeled R, C, W, Y, G or O/B mean a low voltage central system, and its baseboard model is the wrong product.
What the listings get wrong
The Amazon spec tables for the ecobee Premium and ecobee Essential both list "Electric Baseboard Heater" under uses. ecobee's own support page says high voltage systems like electric baseboard heaters are not compatible. Go with the maker's page. The Amazon Smart Thermostat listing is clearer: not compatible with 110 to 240V systems like electric baseboard heat.
ecobee, Google and Sensi all mention one workaround: a pro can sometimes add a step down transformer and relay so a 24 volt thermostat can control the heater. That is an electrician's project, not a weekend swap.
What Mysa needs
| Check | Mysa's requirement |
|---|---|
| Wall thermostat | You need an existing wall thermostat. A dial on the heater itself leaves nowhere to install it. |
| Wires in the box | 4 or more. Mysa says two wire setups are rare, and to check for capped wires tucked in the box first. |
| Load | Listing: up to 1,900 W at 120V or 3,800 W at 240V. |
| Heater type | Electric baseboard, convector, fan forced, radiant ceiling. Not hydronic (hot water) baseboards, not gas heaters. |
| Power type | Single phase 120V and 240V. Mysa says three phase systems are not supported. |
| Wi-Fi | 2.4 GHz. |
- At 120V1,900 watts
- At 240V3,800 watts
Add up the wattage of every heater on that thermostat. The rating plate on each heater gives the number. A line voltage thermostat only controls the heaters wired to it, so a home with five baseboard thermostats needs five.
Hot water baseboards are different
If your baseboards carry hot water from a boiler, the thermostat is usually a 24 volt, two wire, heat only type. That is a low voltage job. Run the wire checker with "heat only" selected, and expect to need a C wire.
Tick your own wires in the wire checker, or compare all seven picks on the roundup page.