It's changed over the years. Currently it's an Arduino Mega2560 with custom stuff to talk to the 1-wire sensors (not just bit banged) and the ubiquitous 8 relay board for output. But the actual thermostat logic is on my main Linux server machine. Yes, if my server crashes my heat goes down, I'll fix that some day, but it never does crash so it's run like this for 12 years. The original setup used owfs for input and output, but it was never completely stable that way.
Why? Because my bog standard 7-day programmable thermostat did not have the "turn the heat up in two weeks just before I come back" functionality. Back in 2008, if internet programmable thermostats even existed, they had the same suckage - only works via proprietary cloud stuff. Yech. I just want "turn up the heat", and I want it my way. The web interface is a HTML form with a single input box that says "Temperature". Programmable thermostat stuff is crontab entries.
Why? Because my bog standard 7-day programmable thermostat did not have the "turn the heat up in two weeks just before I come back" functionality. Back in 2008, if internet programmable thermostats even existed, they had the same suckage - only works via proprietary cloud stuff. Yech. I just want "turn up the heat", and I want it my way. The web interface is a HTML form with a single input box that says "Temperature". Programmable thermostat stuff is crontab entries.