That’s exactly what I did. If HA crashes, the old dumb thermostat will keep the house from freezing.
I don’t have a “thermostat” per say.
Home Assistant controls my HVAC unit via an MQTT controller with 4 relay outputs for heat, cool, fan and humidifier. Generic Thermostats on the HA side manage it.
It’s been that way for nearly a decade.
https://www.aaroncake.net/house/automation/hvac.asp
In the rare event that HA is down or something network related occurs, the old manual thermostat is still connected with a minimum set temperature of 4 degrees to prevent pipe freeze in the winter. This has never been used.
I do use some OpenHASP panels which allow adjustment of the Generic Thermostats however they are rarely touched.
My interaction with the climate control system is mainly forcing on and off away mode if needed.
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I did not n=bother to talk about Hysaerious. All thermostts have this, even my mechanical one. The “heating off” point has to be higher then the “heating on” point. But tht is very easy to do with automations in HA.
In fact with sensors all over the house and a computer I can do better then "bang-bang abd use some kind of feedforward basked on thr current rate of change of temperture.
I think I could define an enelope that has two parameters, devation from desired set point and and frequency of on/off switching and let the system coloect data used to find a ballance of both.
What I am saying is with a computer in the loop, the termostate could be optimal (by whatever definiktion iof optimal you like)
The next step is to introduce “zones” where we divide the house into two zones and try and heat each one independantly. But this is overkill for a place where it rarely dips below 50F even at night.
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My house has three zones. Sometimes I wish it had four. Each has it’s own “smart” thermostat which can run and be viewed or managed locally, or through the vendor’s cloud, or via an HA integration (also through the vendor’s cloud.)
Normally I avoid cloud-based solutions, but I’ve come to appreciate this one. First and foremost, the thermostat has “smarts” which take into account the type of heating and cooling system, and the outside temperature, to maintain a constant temperature, rather than a “bang-bang” upper and lower limit. This also factors in the most efficient cycle times for the system, which impacts both its efficiency and longevity. I have no intention of re-inventing all that logic, developed by HVAC experts at the vendor’s company.
But the other thing it gives me is redundancy. If HA dies, but my network connection is still up, I have an alternate way to manage and view my thermostats. And if both are down, the thermostats still merrily keep their set temperatures and run any schedules I’ve loaded into them.
Many thermostats already contains computers (by whatever definiktion iof optimal you like).
You didn’t indicate that you knew any of this in your original post. To state things as if it’s trivial now is insincere.
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