Smart switching a baseboard heater with no neutral - but built-in

I want to replace the thermostat for the baseboard heaters in my apartment with simple smart relays/switches. I would be using a temperature sensor in the given baseboard’s vicinity to control whether the heater is on or not.

The problem, however, is that I’ve got no neutral at the baseboard heater and I live in an apartment. I’m in North America and we have split-phase systems where a hot and a neutral will give you 120VAC but 2 legs of hot will give you 240V. I have 2 hot legs at my baseboard heater.

So my question is thus: Can I connect any 240VAC-rated smart switch in this baseboard heater’s thermostat compartment or would I really have to pull wires to the heater from some nearby electrical outlet?

As well, are there any standalone devices that are made for this purpose?

This actually reminds me of another user who had 2 way switch for his water heater.
He added 25a contactor to the water heater:

2 way smart switch → 25A contactor → Water Heater

As for your case, i think you could install zigbee switch that doesn’t require neutral & add the contactor.

Look at the mysa:

Wiring diagram in the amazon pictures. Doesn’t look like a neutral is used for 240. You just need to be sure the rated thermostat wattage is above your heater(s). Also popular is the Sinopé brand

Another alternative is using at Aube Technologies RC840T-240 in conjunction with a normal Nest/Ecobee . I may go this route, as the Mysa’s are not rated high enough for my system. There are some youtube videos of how to install it. As you are in an apartment, the mysa or others like it might be best.

edit: sorry, didn’t realize you wanted to put in the compartment and do not have a thermostat. In that case, the Aube might?? fit, then just run some wire out of it to a nest.

I think if I were to go with a solution that requires wires sticking out, I’ll go with something like the Shelly Plus 1 UL with a NEMA 5-15P breakout cable attached to the Line and Neutral terminals that are used to power the Shelly.

The contactor solution + Zigbee solution, I think, is something that I think I’ll explore as a last resort, but with something like the RC840T-240 in place of the contactor as there’s less chance of shorts due to contact with the metal frame. Most contactors I’ve seen have an exposed frame

The reason for such a specific solution is cost. I’d like to keep it as low as possible as right now I’m testing solutions with one heater, then will scale across the rest later on

Ohh man. Each heater is individual and not controlled by a central thermostat? That must be a pain to set them all, I understand why you want a cheap solution.

In the end I’ll be going with the relay plus contactor method:

  • A DPST contactor will be connected between the L1/2 lines and the baseboard heater
  • I will get a TP Link smart outlet => This will only be for testing purposes. The real relay will be based on the Shelly Plus 1 UL as it can be configured to default to disconnecting the power to the contactor should the power go out while I’m not at home
  • The coil terminal for the contactor will be connected to the TP Link smart outlet with NEMA 5-15P breakout cable

This should be the most cost effective and relatively safe solution

Something like this:

Late update on this: The SONOFF BASIC R2 works just fine connected directly to the 240VAC mains.

240VAC L1+L2 to SONOFF BASIC R2 controller LINE and NEUTRAL (input), relay (output) LINE and NEUTRAL to the heater L1+L2


SONOFF BASIC R2 is only rated for 10 amps… how did you have it control the load of the heater?

It doesn’t seem to be in stock or even intentionally promoted on the site anymore, but I got the Mini R3 which is rated for up to 16 amps which none of my baseboard heaters exceed.

I’ve had these running for almost a year now with no issues whatsoever. They’ve been really reliable :smiley: