So DIY solutions exist that raise the cost to an education in computer programming and $50 in hardware...to avoid touching a thermostat four times a year. That's neat.
It's incredibly easy to do (caveat - at least if you're familiar with software dev already).
Most thermostats are literally just digital thermometers that control a relay that turns the furnace/ac on and off.
A simple arduino (or much cheaper IC) can easily do the same thing if you wire it in.
And then on the software side... there's several large, open-source projects that exist in this space and provide nice api tooling for interacting with those devices. Things like:
I'm considering making an OpenTherm controller for my heating boiler, I just researched this topic a few days ago - it's absolutely true, there are ready-made Arduino libraries for that.
I inherited a 1980's model AC/Furnace and controlling the AC at least is extremely simple and cheap. A 12V relay in the compressor housing activating the 220V switch, connected to another relay controlled by a Pi zero which is controlled by yet another PI zero with a $10 DHT 22. A bash script check the temp and activates the compressor via SSh when the temp goes above 74F. The furnace control hasn't died yet so I haven't bothered replacing it.
Putting the cooling system on IoT total cost = ~ $100
What if you charged someone to build and install the same system in their house? You'd probably charge a lot more than $100, and that's what the real cost would be for most people.
controlled heating for my flat with open source and Zigbee compatible devices would cost me ~1k. I did not calculate the ROI but break even looks like it’d take many years.
