Which smart thermostat works with electric baseboard heaters?

Two answers circulate, and both skip the part that decides#

The first answer says any smart thermostat will do with the right adapter, the way a Nest or an ecobee gets around a missing C wire. It will not. Electric baseboard runs at 120 or 240 V through the thermostat itself, and the furnace thermostats switch a 24 V control circuit. ecobee lists line voltage as incompatible on its own checker, as smart thermostats and the C wire explains, and no adapter in the C-wire comparison changes that.

The second answer says any line-voltage smart thermostat will do, so buy the one with the nicest app. That is closer, but it skips the three numbers that make one fit and another fail. The models below differ by 1,000 W in what they can carry, by 500 W in the least they need to see, and on whether they can run from two wires at all. Every one of those differences is published by the maker. It just is not published side by side.

The line-voltage smart thermostats, side by side#

As each maker publishes them, read in October 2026. Watts are the maximum for all heaters on the thermostat combined.

Sources: Mysa's Gen3, V2 and LITE spec sheets and product pages (US prices), Sinopé's TH1123WF fact sheet, TH1123WF and TH1124WF instruction sheet, and its Lite and Zigbee product pages, and King Electric's Hoot WIFI specification sheet. Sinopé also sells a 4000 W Lite (TH1134WF) and Zigbee model (TH1124ZB) with the same 16.7 A and 4,000 W ratings as the TH1124WF.

What the table settles:

1. The low-cost models carry less. Sinopé's TH1123WF, TH1133WF and TH1123ZB stop at 3,000 W. Every other model here reaches 3,800 W or more.
2. The minimum load is the number most people never check. Sinopé's standard models need 500 W at 240 V before they will regulate a baseboard properly. Mysa's LITE states no minimum at all, and the V2 asks for 250 W.
3. Two wires narrow the list to Sinopé's TH1123 and TH1124 families. Mysa says "If you only have two wires, it is a 'switch loop' and Mysa will not work without rewiring." Sinopé's Lite is "Compatible with 3-wire installations only." The TH1123 and TH1124, in Wi-Fi and Zigbee, are listed for "2 or 4-wire installations."
4. Only one model here is sold as double pole. King lists the K902 as "2P", and Mysa states its own design "functions internally as a single-pole device." Why that can matter is below.

How many feet of baseboard one thermostat can run#

Read the watts on each heater's label and add them up. If a label is gone, Sinopé gives a rule: "number of watts = 250 watts x baseboard length (ft)", with the example that "a 6 ft baseboard equals 1500 watts at 240 volts." Sinopé adds that "This formula applies to a 240 Vac installation only."

Applied to the maximums and minimums in the table, at 240 V:

So a living room with an 8 ft and a 6 ft baseboard on one thermostat, 3,500 W by the rule, is over every Sinopé 3000 W model and under the 3,800 W and 4,000 W ones. A single 2 ft heater in a bathroom sits right at the TH1123WF's 500 W floor, and anything smaller is under it.

If your home has 208 V service, common in apartment buildings, the amp figure is the one that holds. King states 3,328 W at 208 V for the Hoot, which is its 16 A times 208 V; the same arithmetic gives 2,600 W for a 12.5 A Sinopé. A heater rated for 240 V also puts out less at 208 V, about 75% of its label by resistance arithmetic (208 squared over 240 squared), so the label overstates the load there.

What the number of wires in the box means#

Turn off the breaker, take the old thermostat off the wall, and count the conductors connected to it, leaving out bare or green grounds.

• Two wires. The thermostat sits in series with the heater and nothing else reaches the box. Mysa calls this a switch loop and will not work on it. Sinopé's Lite will not either. Sinopé's TH1123WF and TH1124WF instructions show a "Two-wire installation" and say "The wires of this thermostat are non-polarized," so these, and the Zigbee TH1123ZB and TH1124ZB, are the models read here that take two wires.
• Three wires. Supply, load, and the other line or a neutral. This is the setup Sinopé's Lite requires, and the one Mysa means by "Neutral or L2 required."
• Four wires. Usually a 240 V double-pole thermostat with both lines in and both lines out to the heater. Mysa Gen3 lists "3–4 wires · same gang box", and Sinopé's TH1123WF instructions show a "Four-wire installation."

A white wire in the box is not proof of a neutral on a 240 V heater circuit, where it is often the second hot line. The neutral wire guide covers how to read what is there. A smart thermostat is also deeper than most dial thermostats (Mysa Gen3 is 1.9 in deep), so check the box has room for it and the wire connectors, using the method in box depth and fill.

Single pole, double pole, and the "off" position#

Mysa says plainly that its baseboard models switch one line, and King sells the Hoot in a single-pole version (K901) and a double-pole one (K902). Sinopé's documents read here state neither. Mysa's baseboard model "requires a connection to both power wires (L1 and L2/Neutral) but only switches the power to the heater on one of those wires (the load wire)." On a 240 V heater, the other line stays live at the heater when the thermostat shows off.

That matters for one reason. The National Electrical Code lets a thermostat double as the heater's disconnecting means only under conditions. Section 424.20(A) of the 2020 NEC, as EC&M summarizes it, requires a marked OFF position, that it "Directly opens all HOT conductors in the OFF position," that the circuit cannot come back on automatically once the device is placed in OFF, and that it is within sight of the heater and accessible. A thermostat that switches one line cannot meet the second condition.

If the old double-pole thermostat was the heater's disconnect, a single-pole smart one leaves the breaker, or another listed disconnect, to do that job. Whether that is acceptable where you live is a question for an electrician or the local inspector, and many jurisdictions require one for this work in any case. King's K902 is the double-pole option among the models read, but its specification sheet does not say whether its off position opens both lines, so this page does not claim it serves as a disconnect.

Fan-forced heaters, in-floor heat and what is excluded#

• Fan-forced convectors (the wall heaters with a blower, common in bathrooms) work with all three brands, with limits. Sinopé allows "Maximum one fan-forced convector per thermostat," raises the minimum load to 1,000 W at 240 V on its standard models (500 W on the Lite), and has a FAN setting for "long cycle" that must be selected for these heaters.
• Contactor or relay systems are out for Sinopé: it "Cannot be used with: A system controlled by a contactor or relay (inductive load)." Every Sinopé rating above is marked "Resistive load only."
• Electric in-floor heat is not a baseboard job. Mysa lists it as not compatible with the baseboard models and sends buyers to Mysa for In-Floor. Its other exclusions are low-voltage 24 V, millivolt (gas fireplaces) and central hydronic systems.
• Plug-in heaters are a different question entirely, covered in space heaters on smart plugs.

Wi-Fi, Zigbee or Matter#

Every Wi-Fi model here uses 2.4 GHz only, which is the band Wi-Fi 2.4 GHz pairing problems are about. Beyond that, the radio decides which hub, if any, sits between the thermostat and your phone.

• Mysa Gen3 is Matter certified and lists Matter, Alexa, Google Home, Apple Home and SmartThings. It is the only baseboard model read here with Matter, the thermostat device type described in Matter device types. The V2 and LITE list Alexa, Google Home and Apple Home.
• Sinopé's Wi-Fi models connect straight to the router. The TH1123WF instructions carry the Works with Apple badge, and its fact sheet lists Alexa and Google Assistant. The Lite lists "Permanent Internet connection" among its connectivity requirements.
• Sinopé's Zigbee models need a gateway: its own GT130, or SmartThings or Hubitat, the three choices its shop offers. Sinopé still lists "Permanent Internet connection" among their requirements. Zigbee mesh behavior and coordinators are covered in Zigbee explained, and the platforms in Hubitat and SmartThings.

None of the documents read say what each thermostat does when the internet is down. The questions to ask are in what still works in an internet outage, and why it depends on where the schedule runs is in local versus cloud control.

Which thermostat, by situation#

Renters should read a smart home for renters before touching a line-voltage box, and anyone buying several should add the wire count and wattage per room to the pre-purchase checklist.

Where this page stops#

• Brands read: Mysa, Sinopé and King Electric, from their own spec sheets, instruction sheets and product pages, as of October 2026. King's sheet was read from a copy hosted by a retailer, Zoro. Stelpro, Honeywell (Resideo) line-voltage models and other brands were not read, so the page makes no claim about them.
• Not stated by the makers: Mysa Gen3's minimum load, the price of Mysa Gen3 in US dollars, King Hoot's minimum load and wire count, and how any model behaves offline. Where a cell says "Not stated", that is what the documents say.
• The code text is the 2020 NEC as summarized by EC&M, not the code book. Your jurisdiction may have adopted another edition or local amendments.
• US and Canadian 120, 208 and 240 V circuits. Mysa and Sinopé are Canadian companies; prices are Mysa's US list prices.