My goal is to automatically turn the heater down to 55 degrees or so after a set time duration (e.g., 2 hours) and/or at a set time (e.g., 10pm), so that the heater does not run because I forgot to manually turn the thermostat knob when I was done working in the garage.
I have not found a programmable thermostat, wireless or not, that will work at almost 32 Amps (7500/240). I did find a Sinopé 50A Zigbee load controller at about $150 which I could pair with a Zigbee thermometer, but the price of the parts plus an electrician puts the price above $300.
So plan B is to find something that is wireless (preferably Zigbee but WiFi is OK) that will attach to the existing knob (or the knob shaft) and allow me to program "55°F" and "68°F" rotation points (about 30 degrees of rotation) on a schedule.
One candidate is this $46 Smart Radiator Thermostat Valve for Zigbee from Amazon, but I don't know if it can be adapted to fit over the knob or knob shaft:
Are you sure your tstat is not low voltage? Seriously doubt the load is run thru it. If it is line voltage I would work in a 24V transformer, then your tstat problem would be solved. After that a 24V contactor. Hard to say for sure without seeing it.
Is this the unit?
That one has a remote control.
If yours does, maybe you could tap into that.
edit: I also remember in the old days that they sold a programmable adapter that used a little heater under the thermostat to fake it out.
Are you sure the heater is 7500 watts? That is very large.
Here is a relay device specifically for electric heaters so you can run standard 24VAC thermostats. You could either run a simple setback thermostat or go all in with a WiFi thermostat.
I use these on baseboard heaters in my basement in Illinois. I have three Aube units controlling three baseboard heaters controlled by two wifi thermostats. Works great going on 8 years now.
If the 7500 watts is for sure then maybe someone makes a higher current version of the Aube RC840T-240??.... Also maybe you could reconfigure the heater for two 3,750 loads and put an Aube device on each leg and control from a single thermostat.
40A definitive purpose contactors are common in air conditioning units. Any thermostat could drive the coil side of a 24VAC coil contactor.
This heater does have an internal thermostat and a remote control -- BUT the thermostat sucks -- it self heats and turns off way before it should. So I had the external thermostat from the same company installed to separate the sensor from the heater.
Even using the remote, it only had a timer option, and then turned power OFF -- disconnecting the internal thermostat. I don't want that, since the garage can get too cold after the timer times out.
That's what the company advertises for the heater. And I use their thermostat -- their blurb:
DR-001 wall thermostat works with single or double poles circuit with voltage inputs from 120-277VAC with 28A maximum power. It can be wired to 3360W@120V, 5824W@208V, 6720W@240V and 7756W@277V heating system with control range of temperature 41F-90F (5-32C). Wall mount design sits flush against wall with large knob allows easy adjustment to all temperatures. Double terminals with OFF position. ETL listing.
BTW, my plan C (or maybe it's D) is to glue a small magnet to the bottom edge of the dial and attach a contact sensor below that so that the contact sensor registers CLOSED when the dial is at 55 degrees, and OPEN for 68 degrees. A Rule can alert me if the sensor is open for more than X hours or past Y o'clock.
You can use 24V smart thermostat of your choice together with high amp contactor with 24V coil. The contactor will control the heater and thermostat will control the contactor.
The sinope are worth the cost. I have an all electricly heated home and have 9 of them. Not wanting anyone to do anything out of their comfort zone, but if you just turn off the breaker to the heater before you start, it’s a simple job. There’s just two wires and the Sinope will come with the quality wire nuts you need. You can watch YouTube videos that’ll show you how to do it as well. It’s that easy. There’s no mixing up the wires because it’s 240 V.
I’m not sure what you mean by extra parts. The new thermostat will come with everything you need.
If you’re at all unsure that the thermostat is compatible, you can contact Sinope support. They’re really responsive and good.
I believe 4000W is their top capacity from the TH1124ZB. I have one of those, but I didn't need it. It is connected to two fan-forced floor mounted heaters, but they only draw around 2580W.
Are you certain your heater draws that much? If it does, you should have a 40amp breaker on that circuit, because 7500W @240v AC is 31.35 amps and the breaker should be sized to handle no more than 80% of the total load.
This is the solution I would use. Just a plug-in 24VAC transformer to power both a regular 24V smart thermostat, and the 24v contactor. Just replace the 240v thermostat with the contactor, and control the contactor with the smart thermostat.
Based on your spec the thermostat is too small for the heater. Maybe heater isn't full 7500 or else you are pushing it with the thermostat.
The problem with line switching thermostats is inaccuracy due to self heating. Due to the large currents the wires and contact points can heat up and throw off the thermostat.
The easiest solution here is to put a 10W resistor just below the bimetallic plate inside the thermostat and power it from a 5-12VDC power cube in turn plugged into a ZWave (or WiFi, or Matter) controlled plug. Turn on the wall cube via Hubitat to heat up the resistor and spoof the thermostat that it is warmer than it truly is. Pick the R value to get the temp drop you want.
By spoofing the thermostat you avoid playing around with the mains power lines and risking making an error or doing something that is not code compliant (NEC) which could void your home insurance. I did something like this 43 years ago when set back thermostats were not so common. I just used a cheap timer switch to turn on the dc supply every night. It was crude but it worked reliably.
This is at tangent to OP's question since no one would actually recommend using one of these things, but in fact you could use it for heating too. In that case, you'd set the heating setpoint higher than you really want and leave the heat strip on around the thermostat on all the time except turn it off when you want heat.
