A while back, I wanted to add smart thermostats to my apartment. However, I was surprised by the lack of inexpensive, line voltage (or baseboard) smart thermostats. Originally I planned to do it all DIY, but I realized there's plenty of cheap, smart wall switches out there, and a line voltage thermostat is just a wall switch with a temperature sensor and some type of UI. Plus, I figured a converted wall switch is probably a bit safer. So I decided to make some. At the time, most smart switches used an ESP8266 so I designed a thermostat that could take advantage of the microcontroller that came with the switch. I've since moved to a house with central heat but has a baseboard heater in the bathroom. I wanted to be able to run the heater on a timer for showers in the winter so I redesigned the thermostat to use a ESP32 for the increased I/O to add buttons instead of the rotary encoder.

Full instructions, CAD, and ESPHome YAML files are over on Github