We have a number of electric baseboard heaters in our house that I would like to smarten up. Eventually I intend to get rid of these baseboard heaters, and replace them with a better heating system, so ideally I want to use Ecobee smart thermostats, rather than a line-voltage baseboard thermostat such as the one from Mysa, so we can keep them for controlling the future heating system (also for other reasons, but this is the one that most justifies the cost).

As far as I can tell, the Aube RC840 series of relays appears to be the best option to enable this, though I’m very open to alternative options.

In my research, I’ve read that it’s possible to use one thermostat to control two baseboard heaters with Aube relays, but I want to know if it would be safe/reasonable to use a single Ecobee for three baseboards (they heat a single, large space, so an Ecobee with a smart sensor or two would work well; another reason to favor Ecobee over Mysa: fewer thermostats).

Also, in such a scenario would I want to use the RC840s with transformers, or without, and use a separate transformer at the thermostat for 24V power?

1 Answer 1


You can have an unlimited number of relays, but only one transformer. (unless you do weird tricks with Rh/Rc).

Well, actually there's a practical limit on relays. The Ecobee will only be rated to switch so much current. The transformer is also typically 40 VA (1.67 amps) and has limits as well.

The Aube relays you specced are 1 VA each. 12 of them would be 12 VA or 0.5 amps. I wouldn't go higher than that without checking if the Ecobee has a switching limit.

Actually since you do not need the built-in transformer, you don't need to stay in the Aube line. You could also use RiB or even specific-purpose-rated contactors, if the specific purpose is control of electric heaters.

  • Well, it sounds like 3 shouldn’t be a problem, then! Thanks! I’ll do some looking into other options for relays, any recommendations on things to look for? Commented Mar 30, 2023 at 1:38
  • Harper covered it pretty well. Mainly have to keep track of the currents used to make sure you don't exceed what the Ecobee or a relay can handle.
    – SteveSh
    Commented Mar 30, 2023 at 2:18
  • @Josh the RiB line is a general-purpose relay that is popular and less costly than Aube. Commented Mar 30, 2023 at 20:13

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