I have two Venstar T2000 thermostats working decently well with latest version of HomeAssistant running on HassOS. One of them works perfectly. But the other one sometimes (for an hour or more every single day) provides temperature readings which bounce up and down by exactly 3 degrees (F). I’m not sure if this is a problem with the thermostat itself, or with it’s API access, or with the HomeAssistant integration.
The erratic temperature readings were causing cooling to turning on and off repeatedly. This forced me to go into the installer settings and increase the deadband value. But that causes significantly less accurate control all of the time.
Because the reading is skipping so quickly by exactly 3 degrees (F) up and down, I’m quite certain that this is not due to the actual temperature of the area fluctuating.
I’ve seen this happening between 70-73 F, and between 77-80 F. I’m not quite sure how simple rounding error in a conversion from C to F would result in those numbers, but I suppose it’s possible?
This brings me to another question… does this model only report temperatures as integer values? It would help a lot for control if it reporting with 1/10th degree precision, but I couldn’t find anywhere that Venstar has provided the spec for this.
If the API could be sending raw integer temperatures in C, might there be some way I could make it send them to HA in F instead, for more accuracy?
Here is a screenshot of the history graph showing the issue. And again, this is what is has been doing every single day since I first installed it.
Did I make a big mistake by thinking that the Venstar T2000 would be sufficient, and that spending more money for basic control wasn’t necessary? If indeed this thermostat always operates in integer C temperature values (whether display is set for F or not), then I would have expected to see a bunch of discussion and negative reviews about this problem, but I didn’t. Maybe I’m the one who needs to call Venstar’s bluff about this cheap model? I really hope that I’m mistaken, and that the issue is addressable! Otherwise I guess I’ll be replacing both of my thermostats yet another time, just to realize the dream of creating my own smart control program.
By the way, I haven’t yet tried to watch the display on the device itself to see if the same unbelievable numbers are appearing there.
I ended up just ditching the Venstar thermostat temperature readings entirely.
Instead, I’m now using Shelly Plus H&T for more accurate (tenth-of-a-degree) readings. The trick is to write an automation that uses those external sensor readings to control the thermostat indirectly. Instead of directly setting the target temperature on the thermostat, I now have a “virtual target” which is just an HA sensor entity. The automation compares the external sensor reading to the “virtual target” and sets the thermostat to a super high or low value.
This basically puts my custom code in full control of the HVAC action, with the hardware thermostat itself providing other more basic and critical functions such as managing the fan together with cooling/heating, etc.
Of course this setup also enables me to extend to unlimited numbers of external sensors in different locations. (And those sensors can be far less costly than Venstar’s own external sensors!)