I'm installing a small baseboard heater in a back bedroom, adding it to a 240V circuit with two heaters already installed in other rooms. I mainly use the two heaters on low when I am away to prevent pipes from freezing. I heat with wood when there. I would like to be able to totally cut off power to the newly added third heater. This bedroom gets closed off when I am away and since the heater has a built in thermostat with lowest setting of 32degrees it will likely come on when the room is closed off. I don't need or want that...waste of electricity! No pipes back there. I would like to install a switch to the line before it reaches the heater to simply cut the power to that back bedroom heater when I'm away.

Would there be any issues with this type set up?

Do I need any special kind of switch or will a basic 20amp 120/240V light switch do the trick? Thanks.

  • Get a 20 amp 2 pole switch such as: amazon.com/dp/B003AUIDMY/ref=cm_sw_r_sms_c_api_Fq6qAbYQQM3XP – Tyson Dec 27 '17 at 13:46
  • if a two pole is required here someone should write that up as an answer with a good explanation. – agentp Dec 27 '17 at 14:23
  • yes, curious why I would need a double pole for this? I only want to cut power to one heater and would place the switch in line running to this third heater. The other two heaters want to be unaffected by the switch. Wouldn't this work fine? amazon.com/dp/B002MPPTAC/ref=psdc_6291359011_t3_B003AUIDMY – Margaux Lechat Dec 27 '17 at 14:50
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    I will say "not a dup" on this as the other question is more complicated. – agentp Dec 27 '17 at 16:20
  • Or you could get a thermostat module with an "off" switch. Or you could get an external light switch style thermostat which contains an off switch; they are about $10. An on-the-heater 'stat isn't that reliable, it's too close to the heater. – Harper - Reinstate Monica Dec 27 '17 at 17:01

Yes, you can do that if the switch is a double pole switch rated for 240 volts or higher and is rated for the current of the heater. The National Electrical Code requires that the switch be rated for the load it serves. This means voltage AND current.

There are also line voltage thermostats with a positive OFF position so you wouldn't need the switch.

Whether you use a single pole or double pole switch it will work the same. It is a single phase circuit and it will work either way. However, the Code requires that the switch disconnect all ungrounded conductors. See below.

The difference is, with a double pole switch you are breaking the circuit in two places at the same time instead of one. This reduces the amount of pitting on the device contacts. With a double-break device the contacts will last longer at any given voltage. At 240 volts contact pitting is much higher than at 120 volts.

Additionally the National Electrical Code requires that all ungrounded conductors to fixed electric space heating be disconnected:

424.19 Disconnecting Means. Means shall be provided to simultaneously disconnect the heater, motor controller(s), and supplementary overcurrent protective device(s) of all fixed electric space-heating equipment from all ungrounded conductors.

(C) Unit Switch(es) as Disconnecting Means. A unit switch(es) with a marked “off” position that is part of a fixed heater and disconnects all ungrounded conductors shall be permitted as the disconnecting means required by this article where other means for disconnection are provided in the types of occupancies in 424.19(C)(1) through (C)(4). ... (3) One-Family Dwellings. In one-family dwellings, the service disconnecting means shall be permitted to be the other disconnecting means.

So, a 240 volt circuit would require a two pole switch if it used as a disconnect for the heater.

Good luck!

  • 2
    A double pole is also safer, with a single pole switch there will always be 120v inside the heater. NEC 424.19.c says a switch can be used as a disconnecting means if it is marked with a "off" position. – Ed Beal Dec 27 '17 at 23:21
  • @EdBeal thanks for the Code reference Ed I added that to my answer. – ArchonOSX Dec 28 '17 at 9:28

They make 1- and 2-pole switches rated for 20A and 30A, go with what your breaker says. And those are rated for 240V. 20A's tend to have a red body, 30A's tend to have a green body.

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But first, look at the heater's onboard thermostat. It may already do what you want. It is fairly likely that it has a positive "off" switch at the extreme low position, past a detent. Often people never realize it's there, either because the detent is subtle and they aren't really trying to feel it, or the detent is quite stiff and they are reluctant to push past it. Below that detent, it is definitely off. This is more likely if it's a 2-pole thermostat (4 wires).

enter image description here

They also make external thermostats for 240V heaters. These typically have 2 poles, but each pole works differently: one pole is switched by the thermostat, and the other pole is switched by the on/off switch (just as I mention above with the detent).

enter image description here src

If it is a Cadet or similar heater, check to see if it has an optional thermostat module or switch that will do what you want, such as the pictured one above. It is one of several accessories Cadet sells for each end of their heater. One is a receptacle panel, designed for fitting a 120V convenience outlet - maybe you can find a switch that will bolt in where the receptacle goes. Or here's an odd one: an outlet and a switch to allow the user to select heater or outlet (it's a 240V outlet, hence the funny appearance). Obviously that turns off the heater!

enter image description here

If it's a single receptacle like that, I might buy the plate with the receptacle, unbolt the receptacle, and bolt up a switch with a cover plate in its place. Mount that on the opposite end from the thermostat.

  • I never had a moment to thank all the folks for the answers. So thanks. Very helpful. – Margaux Lechat Mar 24 '18 at 0:18

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