It can be done, but the button pushers are very expensive, about $49 for each button, plus $89 Bridge, plus an annual cloud fee. I used to recommend these for some use cases when it ran locally and there was no annual fee. Now I mention it so people can take a look, but I don’t recommend it for most set ups just because of the cost.
I have several space heaters that I took this approach (might work for you…)
Install Smart Temperature Sensor
Install Smart Plug
Plug Heater into Smart Plug
Set Heater on Highest Setting
Use SmartThings to Turn Smart Plug On/Off Based on Temperature from Smart Temperature Sensor
I have another SpaceHeater where this approach did not work because the heater would not revert to power on once power was restored. Always had to hit the on button. I could have setup some kind of IR remote but it was easier to just find another space heater…
For direct wired this depends on the voltage. If it’s simple 110/120 then a good relay would work. For higher voltage 240v then there’s a high voltage relay available from aeotec and I think GE has one that are both z-wave. Use those in combination with temp sensor to turn on/off the heater. For non z-wave insteon has a good relay for 240v usage. I’m thinking of adding insteon into my setup for this same type of project work (excuse for new toys).
I’m not aware of any tutorial out there. If it’s a standard wired setup then it would be the same as wiring in any relay to any other device like a light or fan. Each relay is different in the wiring but they have good instructions and there’s plenty of people on this forum to help with wiring.
Basics would be:
What voltage are you working with? If you don’t know you MUST find out first.
If standard 120v household wiring then I would say to go with a Quibino or Fibaro relay. They are higher quality than say a vision or monoprice relay. You want high quality in the event of relay failure. Mostly to save the work/effort of having to rip it out and replace it anytime soon. I know Quibino has some rated for fan use if your heater is forced air (has a fan).
If you’re working with 240V then you need a higher capacity relay. The Aeotec relay or GE relay would work for this. There may be others in z-wave that I’m just not aware of. I’m assuming you are using SmartThings as that is what forum you’re on. ST doesn’t have support for Insteon otherwise I would include that as well.
Unhook your device and splice/wire in the relay between the main lines and the device lines. Turn on power and pair the relay to your hub. Then close everything up.
Setup your temp sensor in an area and have it working with ST
Create a rule with Webcore (maybe smart lighting could do it, not sure) that if temp is below a threshold then turn on the heater and if above a threshold turn off the heater.
My suggestion is to run a new 12/2 wire from the heater to a new junction box on the wall above the heater and install a smart line-voltage thermostat instead of messing around with all the bits. Sinope and Stelpro have smart thermostats that are compatible with Smartthings.
In the heater you could just wire past the internal controls so it’s only controlled by the new thermostat.
The reason not to use strictly smart controls is uptime. If you’re using smartthings as your heater scheduler, and you lose internet connectivity or there’s downtime, your heater either stays locked on, or off, until the system is restored. Not ideal.