You don't need a Jbox for a baseboard heater. The hole in the wall is fine. They have a built-in box. All you need is a box connector to connect your 12/2 cable, no need for 12/3. Because it's 240V, no neutral is used. Check the wattage of the baseboard to determine the cable and breaker size. You may only need 14/2 15A. In my jurisdiction, you can have a receptacle above a baseboard. It's not a great idea, but here it's not against code. Check your local codes. What about your thermostat? Wall mount thermostats are MUCH better than 'stats mounted directly on baseboards. They are way more accurate as well as easier to use. Get a double pole thermostat if you want to be able to turn the heater off completely, rather than using the breaker as an on/off switch.

Thanks..thanks for the tip on the thermostat. Are the double pole thermosats a Home Depot type of item...or should I look elsewhere?

I bought a double-pole thermostat at Home Depot about five years ago for roughly $40, as I recall. It's rated for 25A and I installed it on a 20A (12AWG) 240V circuit. Works like a champ.

As of that time (and note that I have not updated my info since then), receptacles placed above baseboard heaters were categorically forbidden in my jurisdiction in Northern Virginia. (I remember this for certain because I had to remove an outlet to pass inspection.)

After doing some poking around to find a conclusive governing NEC code article, my tentative conclusion (and take it as no more than that) is that in most jurisdictions, it appears to be more a matter of UL listing than NEC code per se. That is, for some electric baseboard heaters, manufacturers state that receptacles may be placed above their heaters while others give installation instructions precluding outlets above their heaters.

A couple of weeks ago, the subject came up with an architect/GC friend of mine who claimed that a local inspector told him that the basis of our county's ban was a local interpretation that receptacles installed above electric baseboard heaters posed unacceptable dangers to lamp cords and other plug-ins, regardless of whether the installation instructions allowed them.

Go figure.

Because I've read many conflicting opinions on this issue, it strikes me that this is one of those questions that is best resolved by consulting the AHJ, armed with the specifics of the manufacturer's installation instructions.

Others may have another take on this and, if so, I'll be interested in reading any additional replies.

matt, just remember that if you decide to coil up the wire in the wall for future use, it doesnt get hooked up to a breaker, or even enter the breaker box. i know it sounds stupid, but there are people out there that would hook it all up and just coil the wire, live.

and it doesnt matter if the heat was added later or not, you still cant have an outlet ABOVE the heater, so maybe plan for that now.

DOH! 2005 NEC 210-52 (enumerating required 15- and 20-ampere receptacle outlets)...

(e) In every kitchen, family room, dining room, living room, parlor.... No outlets may be installed over an electric baseboard heater.