Hello, first time poster. I’m looking for thermostat recommendations. Want to keep the communications as local as possible. Other than that anything will be a step up from the dying thermostat we have. I’m not sure what other factors to consider.
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What kind of thermostat? Room thermostat for floor heating? Radiator thermostat / TRV?
If you control your heating from Home Assistant already, I have had good success using MO-C401 room thermometers as temperature input and using HA to set the target temperature …
I didn’t know there were multiple kinds. The one we have now connects to a furnace and ac. It came with the house. We don’t have any HA control as our current thermostat doesn’t have wifi or anything we are aware of. It has six pins G W C Y R and Rc with both Rs being connected at the thermostat. Its a honeywell th6110d1005
I have no idea what control those wires you quoted need, but if it is some kind of binary on/off system, you don’t need a thermostat at all. There’s one built-in into HA, and it only needs some kind of connected thermometer and some kind of connected on/off switch.
See Custom smart thermostat: Aqara + Shelly, would these work for me? - #3 by HenryLoenwind
If it needs some kind of analogue signal (resistance or voltage) you can make it work with HA, but you’re on your own converting the difference between set temperature and actual temperature into a signal. If it needs some digital signal, things can go any way.
ok, quick google got me this:
Terminal Designations
G Fan relay.
W O/B Heat relay or changeover valve terminal for heat pumps.
C Common wire from secondary side of cooling system transformer.
Y Compressor contactor.
R Heating power. Connect to secondary side of heating system transformer.
Rc Cooling power. Connect to secondary side of cooling system transformer.
So it looks like a number of on/off switches. Which would mean, you need something with up to 3 dry contacts (relays) to control your system (Rc-G, R-W, Rc-Y ?).
This is a fairly standard whole-home thermostat wiring scheme, at least in the US. The ‘R’ wire(s) provide 24Vac and the thermostat closes relays to energize the G, W, and Y wires depending on whether you asked it to heat, cool, or just run the fan. If you have a ‘C’ wire, that’s a common return (like a Neutral) which can be used to power a smart thermostat (though many have batteries).
A thermostat is fundamentally just a thermometer, a switch, and a user interface, so in-floor heating and thermostatic radiator valve (TRV) controllers count as thermostats. You can even create a “virtual” thermostat within HA and use the web as your UI.
Z-Wave and Zigbee devices are always fully local — Honeywell T6 is quite popular. Matter also works locally on WiFi or Thread networks; several are on the market now but only a few have the wiring you need (check out the Meross, that looks promising). The vast majority of WiFi devices require a vendor cloud account to function, with the notable exception of Ecobee devices which can function locally if you join them to a HomeKit controller. There are also Integrations for Venstar and RadioThermostat, which both have local WiFi APIs (but the latter is no longer manufactured).
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