This is one of the reasons I am working on an enclosure-compatible open-source version of the 2nd gen Nest thermostat. It reuses the enclosure, encoder ring, display, and mounts of the Nest but replaces the "thinking" part with an open-source PCB that can interact with Home Assistant.
Nest Thermostats of the 1st and 2nd generation will no longer be supported by Google starting October 25, 2025. You will still be able to access temperature, mode, schedules, and settings directly on the thermostat – and existing schedules should continue to work uninterrupted. However, these thermostats will no longer receive software or security updates, will not have any Nest app or Home app controls, and Google will end support for other connected features like Home/Away Assist. It has been pretty-badly supported in Home Assistant for over a year anyway, missing important connected features.
I've got the faceplate PCB done and working; the rotary encoder and ring working; and the display working but with terrible code with a low refresh rate.
I need to ship by October to beat the retirement date. Plans to get some regular development report-outs and pre-orders are coming quite soon.
It's open source, and uses ESP32-C6 so it can be Wifi, BLE, or Zigbee, whatever software you intend to load onto it.
I don't know what needs to happen under the hood, but as someone with a Mitsubishi heat pump, if you could demonstrably make it a Kumo Cloud-beater, you'd probably increase sales. Mitsubishi supposedly has the best hardware out there, but their cloud solution S U C K S . . .
You can't even connect it to WiFi with an iOS 18 device due to a so-called "known issue" with iOS 18's Bluetooth architecture. Like what, I'm supposed to buy a new Android device just to hook up your dongle?
Supposedly there's some secret sauce their proprietary thermostats have that third-party ones don't to increase efficiency, or that's what the sales guys claim.
It looks to tick a lot of boxes but isn't quite what I want, and is just expensive enough that I haven't pulled the trigger to test one out anyway. It seems to be well regarded if it does what you're looking for.
(I really only want to add wall thermostats to a new-built house that was designed for mini-splits for the beginning, so it has crappy remotes but no wall thermostats, and to have some button I can press for "all off" to make sure all the mini-splits are actually off. Other features welcome, but those are what I'm really after.)
I was just looking for something almost exactly like this, I have 4 mini-splits, so Arizone would be ~$1,000. This uses the CN104 and looks like it does what Airzone does at ¼ the price. I’ll gamble on one.
This sounds really interesting! I'd love to see it when you're done.
I wasn't aware that my Nest thermostat was going to be End of Life'd, but I just finished replacing it with an older Honeywell/Zwave combo due to lack of features and general de-googleing. Would be great to do something with the hardware, which is really slick.
The goals have been 1. to help recycle hardware and keep it out of a landfill but more importantly 2. to have an open source thermostat with beautiful design. Nest cared a lot about the aesthetics. as do the people with whom I share my living space and for whom a thermostat has a minimum prettiness acceptable. The Honeywell/ZWave landscape has not shown itself to be "pretty" to me for the most part.
Oh I love it, I drew some inspiration for rotary encoder options from here actually. It reminds me of the older Senic Nuimo from about 10 years ago with a similar goal.
Reusing the Nest is about keeping bill of materials cost very low by reusing old hardware, and not complicating the supply chain with PCB manufacturing plus 3d printing plus metal CNC.
Even better, I want to do a "swap shack" style where you buy a refurbed, built model and ship us your old model, which we can then refurb into the next user's home.
Nest Thermostats of the 1st and 2nd generation will no longer be supported by Google starting October 25, 2025. You will still be able to access temperature, mode, schedules, and settings directly on the thermostat – and existing schedules should continue to work uninterrupted. However, these thermostats will no longer receive software or security updates, will not have any Nest app or Home app controls, and Google will end support for other connected features like Home/Away Assist. It has been pretty-badly supported in Home Assistant for over a year anyway, missing important connected features.
I've got the faceplate PCB done and working; the rotary encoder and ring working; and the display working but with terrible code with a low refresh rate.
I need to ship by October to beat the retirement date. Plans to get some regular development report-outs and pre-orders are coming quite soon.
It's open source, and uses ESP32-C6 so it can be Wifi, BLE, or Zigbee, whatever software you intend to load onto it.