Anyone have any expert, or otherwise, knowledge on this?
The real temp in the house was 72. The system is set to 70. I turned off the system power for maintenance work. When power was restored, thermostat, an Essential model, said it was recalibrating, showed 56, approx, as the temperature, and started the heat. It took, approx a half an hour or so to finish recalibrating, all the while the heat was on. Repeatable.
Seems quite lame to me.
There are a few things were Ecobee is quite lame. This is one of them (and humidity measurments are another). As someone who does metrology as a day job, it seems unnecessary to have to have a recalibration after every reboot. Most other temperature systems (non HVAC) that I have ever worked with have a way to store constants in non-volatile memory and reuse them after disconnection from power. This just appears to be a poor engineering decision by the manufacturer.
It should NOT be running the heat while calibrating though. It should be disabled. The fact that it is showing 56 instead of -500 or N/A is problematic.
Thanks. I believe I saw that post.
I agree. The equipment should not be running while calibrating.
I'll call Ecobee and see what they say.
I've had a number of smart thermostats, including the Ecobee Si's,(?), which did not do this recalibration exercise, at least obviously.
Please post your response from Ecobee.
I opened a case.
The gist of their response is something along the lines of: "that's the way it's supposed to work". Maybe they'll elevate it to someone who actually knows something, but I doubt it.
In my experience, good luck with that. They kept trying to blame my humidity issues (10 and 15% off compared to calibrated - in an ISO 17025 accredited calibration lab - devices) on the air flow in the wall behind the stat. Only, that wasn't an issue because I created 3D Printed backplates that Isolated the back of the stat from the wall. When I let them know that, they then suggested I buy newer versions.
My initial contact with them had just been to allow offsets greater than 5%, since there were known issues such that they had to put FAQ's up on how to cover the hole in the wall behind the thermostat (even though it is not a widespread issue on other brands/models when I looked it up). In any case, I now just ignore the humidity on the ecobee and use averages from other devices placed throughout the house. I would only recommend ecobee moving forward as a way to have local wifi control. However, if I ever have to replace, I will be finding something else. Nothing like being gaslit by a company that you gave money to and funny to see the responses when they do not know they are talking to someone who has worked for almost 40 years in the metrology field.
Their smart algorythms and eco+ features I find to be useless for the most part.
My concern is operating during a power outage, where there is generator power coming on an off, maybe for days. You would also think that maintenance techs would have an opinion on it. What the heck is it "re-calibrating" anyway, that requires lack of basic function upon power return? Couldn't it be done in the background while using the last known good values? Whatever. I think it is what it is. I'm not going to put the thermostats on a UPS though, lol.
edit: Speaking of generator, maybe if everyone had a Generac standby generator, this wouldn't be a concern. Ecobee is owned by Generac, btw. 
So, temperature sensors aren't "inherently" accurate regardles of the type of sensor that they are. Most have a known curve for either resistance or millivolts (depending on the type) and require an offset (and sometimes an adjustment on another point in the curve). Almost all devices that work with these type of sensors store those corrections at each calibration in memory that does not get erased when powered down or gets turned off. Apparently, ecobee decided not to go that route and requires these constants to be updated everytime it loses power. I am not sure where they get a reference temperature to compare it to (some devices using thermocouples compare against an electronic cold junction temperature). I have read that ecobee gets the information based on location and cloud connection to weather stations. This doesn't make sense to me, since it is highly unlikely the house temperature is the same as the outdoor temperature. So, I am thinking there is some bit of an internal reference. This jives with the taking 20 minutes to calibrate since you want the system to warm up to operating temperature before you calibrate.
In either case, this is correcting whatever inherent errors are in the built in sensor so that the temperature reads relatively close to what it actually is in the room. And AGAIN, this could be solved by storing the offsets and constants in a memory type that survives a power outage. But, that is not how they chose to design it.
And then do the recalibrating in the background and correct if necessary when complete.
I'd be interested if all the new model Ecobee thermostats do this.
My Essentials are the cheapos in their lineup, after all.
I have an Ecobee Enhanced and I have never noticed it doing this after a power outage. Not saying 100% it doesn't but I haven't noticed it if it does.
I also simulated a power outage by popping the thermostat off its base for a couple hours and then popping it back in. Don't have to go to basement to throw a breaker, lol.
I just remodeled my living room where the thermostat is located. I done the same and removed it from its base for a couple hours for drywall work and painting. When I reinstalled I did not notice anything about calibration. This weekend if it isn't going to be really warm here I will try it and pay attention to see if I see anything. If it will be the WAF will be very low so that would be no go. Lol. I will let you know.
I have had an ecobee3, an ecobee3 lit, an ecobee enhanced, and an ecobee premium. None of them have done this. Something is wrong with your thermostat. I would escalate the matter with Ecobee Support.
Forgot to add, recently, I have been doing a fair amount of work that requires me to turn off the air-handler breaker for up to 1 hour at a time. Never noticed it recalibrating.
My older Ecobees did not do this.
I do have the Hubitat integration running, if that could be a factor...
My Ecobee 4 does this everytime I lose power for more than a minute or two. It has done thise since day 1. ( I should say BOTH of my ecobee 4's do this).
I have two Ecobee 3 Lite thermostats. I believe there must have been a firmware update in the last year or so that added this automatic calibration. I have seen it occur recently during my HVAC equipment changeout. It is annoying as it adds a delay. However, while the calibration routine is running, the thermostat has never called for Heat, Cool, or Fan from the system. Everything just stays off until the calibration is complete.
Funnily enough, I have not seen this with the ecobee premium that I currently have. So it must happen very rapidly.
I think it is related to how long the unit is without power. I am thinking one of two things (or both) could contribute:
If the unit cools down, it will take longer to stabilize. Even if the sensor isn't calibrated, they can wait for the rate of change to stabilize. Longer time off equals longer time to stabilize.
Depending on the internal circuitry (which I am 100% guessing here), there might be some residual charge stored (caps, etc) that allows it to retain calibration constants for a limited amount of time. So, the longer it is off, the more likely to require recalibration.
I can say that we have had outages that were only 5 minutes recently, and I noticed the recalibration on startup
On my Essential, the "recalibrating" message itself is very fleeting.
Download the Hubitat app
