Read more here for step-by-step instructions! This tutorial aims to teach you how to install smart thermostats for your line voltage baseboard heaters using an electric heat relay.

I only recommend products I would use myself, and all opinions expressed here are my own. Product links below may be affiliate links from which I may earn a small commission.

Tools needed:
Wire strippers - https://amzn.to/3PGrrzl
Drill - https://amzn.to/3rdzo4M
3/4" Spade bit - https://amzn.to/3pu0Mew
Screwdrivers - https://amzn.to/3JznU28
Pliers - https://amzn.to/3NzTEVJ
Wire nuts - https://amzn.to/3PDsLmx

Products:
Amazon smart thermostat - https://amzn.to/3r8OVD7
Aube Electric Heat Relay - https://amzn.to/3NTMpJF
Low voltage junction box: old work (remodel) - https://amzn.to/44ogTJb
Low voltage junction box: new work (access to studs) - https://amzn.to/3XAxcRi
18/5 thermostat wire - https://amzn.to/3rb6AtX
(Maybe) Baseboard heater - https://amzn.to/44qXV4N

I should have included a diagram in the video. Here is a written description, for a project where you're cutting into the wall:

1. A 240v breaker at your circuit breaker box supplies power to one or more 240v baseboard/wall heaters

2. The power cord for an individual heater needs to be located inside the wall (preferably right next to a stud)

3a. Because of stud & wire location, it'll be easiest to mount your thermostat & relay above your heater so that all the wiring is in the same stud bay/section. Otherwise you'll have to open up more of the wall and drill holes through studs to run wire through studs.

3b. Identify where you want your thermostat to be, and drill a very small hole for your thermostat wire to come out of. Your thermostat will sit right on top (in front) of this wire.

4. Cut a hole in the wall for a junction box (as seen in video), preferably in an inconspicuous spot, very near to the thermostat wire.

5. Insert thermostat wire (with a lot of extra, so you've got plenty to work with) into the small hole, and run it to the junction box cutout.

6a. Because you'll need enough length in the 240v power wire to strip it and make new connections, you may need to run new wire to the heater. I recommend removing the heater, pulling up/out (through the junction box hole) the power cord that went to it, and cutting it to give yourself long enough wires to strip and connect. Run a new piece of wire from the junction box cutout down to the heater cutout, again leaving enough length on both ends (wire sticking out) for the new connections, as seen in the video.

6b. Per 6a, split the 240v power wire and run both ends (the wire from the breaker and wire from the heater) to the junction box cutout.

7. Attach your relay to the junction box as seen in the video.

8. Connect the thermostat wire to the relay as seen in the video.

9. Set your junction box in the wall, pulling in the wiring from both the breaker and heater.

10a. If your 240v wiring has just a black, white, and copper wire, then both the black and white wires are "hot" and should be connected as seen in the video.

10b. If you've got 4 wires, with two blacks or red and black + white and copper, then your non-white/non-copper wires are probably hot, and your second hot wire will take the place of the white wire in the video. It's worth using a voltage tester to double check which wires are hot.

11. Connect the new run of wire from the junction box down to the heater cutout, to your heater, as seen in the video.

12. Connect your thermostat wire to the thermostat as seen in the video (may vary depending on your 24v smart thermostat)

*NOTE: In the video, over the final minute or so, the left white wire is 12gauge wire coming from the circuit breaker, through a stud, to the relay junction, and the left yellow wire is 12gauge (exactly the same as the white) going from the relay to the heater. You can ignore everything else (wiring, junctions, etc) to the right of the thermostat.

Baseboard heater image credit
https://www.flickr.com/photos/8663929... - baseboard photo
https://www.homespothq.com/ - creator
https://creativecommons.org/licenses/... - license