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We're renovating a 30 year old home in the US and replacing three 240 volt electric baseboard heaters with new, modern heaters.

Currently, each of the three 15+ year old heaters are wired into their own "dumb" analog thermostats on the wall. We're looking at possibly replacing these with "smart" heaters like these which have an onboard thermostat, and then can be centrally controlled. enter image description here

As I understand it, these new heaters should not have a thermostat in the wall; they should be connected directly to the breaker box. And I believe that currently 240 volts run from the breaker box to the thermostat in the wall and then from there to the heater. If that's correct, can I simply remove the thermostats, connect and cap the wires, and replace them with blank panels? Or would I need to run all new cable directly to the new baseboard heaters?

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Your plan to connect the wires bypassing the old thermostats is a good one and it is code legal.

Make sure to turn the breaker(s) off and test to be sure both legs are off. I have found some 240 volt units that the thermostat only opened one leg.

Make sure to use the proper size wirenut or insulated crimps for the size and type of wire. If aluminum wire is installed, make sure to use deox / noalox or some other type of inhibitors and the connectors rated cu/al for the size wire.

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  • Many 240V units operate one leg thermostatically, and the other leg when you turn the knob all the way to "off". Super maddening when trying to use one to switch two separate 120V circuits.
    – Harper - Reinstate Monica
    Commented Sep 10, 2017 at 20:49
  • Interesting @Harper -- how would I be able to determine if the current thermostats we have operate like that?
    – Josh
    Commented Sep 10, 2017 at 21:29
  • Opening 1 leg of a 240 circuit is what I warned about and very common in days past. Open 1 leg and there is no path back to the supply but it can spoil your day if the breaker is not off.
    – Ed Beal
    Commented Sep 10, 2017 at 21:56
  • @Josh check the instruction/data sheet for the device, it will say clearly. Or ask the manufacturer. Or set it to a temperature above "off" and touch all terminals with a non-contact tester.
    – Harper - Reinstate Monica
    Commented Sep 10, 2017 at 22:44
  • Ah, I see what you mean. Thanks Ed! @Harper I'll research but these thermostats and heaters are over 20 years old with no manuals available. (This is in a house recently purchased)
    – Josh
    Commented Sep 10, 2017 at 22:47
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You don't want thermostats on the heater! That's a strategy done to make the heaters cheap, not better performing. The thermostat is feeling air coming off the heater, not air in the room, and so it won't regulate nearly as well as an external thermostat in a normal location.

That said, it's easy to control electric heaters with 24V thermostat systems like you use for gas furnaces - and that opens you up to using almost any of the "smart thermostats" now on the market, with all their features and connectivity -- as opposed to being "married to a single vendor". You switch the 240V with the same large relays used by thermostats to control air conditioning units (those take 30A @ 240V, and they switch both poles, so they work great). They simply need to be installed in a large junction box, or inside the heater.

If it's practicable for you to run new wiring - or at least bypass any unnecessary detour to the old thermostat - I recommend you do so. Electric heaters place a hefty load on the wires. If your wire length is longer than it needs to be, your heater performance is reduced. Some of that is lost in heat (in the walls, not useless, but not what you are trying to do).

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  • Thanks. The goal is definitely not to have thermostats on the heaters, the goal is to have smart heaters controlled by remote thermostats. Currently, the wired thermostats are located directly above the baseboard heaters, which makes no sense either.
    – Josh
    Commented Sep 10, 2017 at 21:28
  • Some of the newer PID thermostats on the unit are many times more efficient and programmable where the old bimatalic stats are just that 1920's technology some think that is better because its on the wall , Oregon used to have dirt cheap electrical heating and I have remodeled several of my own homes with both gas and electric plus many updates to others and the worst controller on the market is the old adjustable bimatalic stat on the wall.
    – Ed Beal
    Commented Sep 10, 2017 at 22:03
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Another idea is to replace the thermostats with "smart" line voltage thermostats (like https://casaconnect.com/caleo/?v=7516fd43adaa). Then you can just replace the thermostat without needing to replace the heaters themselves. And, if you do replace the thermostats, then you may not need to run new wire.

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