I don’t know if this is possible, but has anyone removed their thermostats from the wall and used home assistant to manage their HVAC? My thoughts would be to use temperature sensors in the house, a tablet powered by the thermostats power source and have home assistant connected to the HVAC system to control everything. If anyone has done this I would like to know about it.
I wouldn’t advise doing this. If your Home Assistant server crashes the heat could fail to come on while you’re out of town and leave you with extensive damage from frozen pipes in some climates, or worse it could become stuck on and leave you with an enormous energy bill or a burned down house. There are thermostats that can integrate with Home Assistant and allow you to control them, I have a Venstar T7850 that I’ve been reasonably happy with so far, it is designed to work with their cloud service but it has a local API and can be used without cloud access. If you are not in North America there are a other options.
I am planning on doing this, but as James mentioned, doing it wrong can be disastrous.
My plan is to use timer relays and sensors, plus a redundant control system that monitors the duct air flow temp. The entire thing will be controlled by an industrial control unit with 6 relays, plus the timer relays.
The purpose of the timer relays is to require a heartbeat from the controller (HA) in order to keep the thing operating outside of its failsafe mode, each heartbeat resets the timer, if it misses one the relay will cut off HA from control.
A good failsafe temp range is heat on at 60 off at 65, cold on at 80 off at 75, keeping a house in a safe range for pets and humans alike.
The control hardware talks to HA over Modbus and operates the power relays which turn on the heat, aircon, and blower. A 4th relay is more of an on/off controller, and the 5th is a bypass for failsafe control, which is triggered by the timer relay. An additional timer relay turns off heating and cooling components in a cycle the same way a wall thermostat does.
I also have multizone control that I dont use, which could also be handled by additional relays quite easily, I turned it off because one of the duct motors caused the air to whistle when it shut off one of the zones.
A duct probe would also alert if a system component fails, like if you turn on the aircon but the air does not get cold, for example, and a small air flow meter on a duct to alert blower failure.
That is a very good point that I did not think of. Thank you
If I were going to do this I think I would keep a conventional thermostat installed somewhere as a failsafe and then let HA do the day to day control. A basic old fashioned analog thermostat set to say 50F would kick in if the temperature ever got that low if you live in a cold enough climate where frozen pipes are an issue, or a similar thermostat set to 80F or so that will cut out if the heat gets stuck on.
Did this 3 years ago. My “thermostat” consists of an Arduino Uno with Ethernet and 4 relays shield mounted inside the furnace. Decidedly temporary until I determine how it will become permanent.
Relays take place of the wall mounted thermostat. Responds to MQTT calls for cool, heat, blower and humidifier.
Wall thermostat is gone. Well, I lied. The wall thermostat still sits there with only heat connected, and set to 4 degrees C as a fail safe just in case. Plus it has a clock on it and I find the clock handy. This thermostat will eventually go away and just a simple fallback thermostat will be mounted to the furnace, set to 4 degrees.
All control is done via HA UI using generic thermostat(s). And it’s not like once it is set, it ever needs to be changed. Just a few automations to switch between home and away modes, heat and cool modes.